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UNITED  STATES  DEPARTMENT  OF  AGRICULTURE 
BUREAU  OF  PLANT  INDUSTRY 

Office  of  Cotton,  Truck,  and  Forage  Crop  Disease  Investigations 
Washington,  D.  C. 

pb  . 


HANDBOOK 
OF  THE  DISEASES   OF   VEGETABLES 

OCCURRING  UNDER  MARKET, 
STORAGE,  AND  TRANSIT  CONDITIONS 

By 

GEORGE  K.  RELINK  and  MAX  W.  GARDNER 
Prepared  under  the  direction  of  W.  A.  ORTON  and  W.  M.  SCOTT 


Preliminary  Edition 

Printed  for  the  nsa  of  the  Food  Products  Inspectors  of  the  Bureau  oi  Markets 
Not  available  to  the  public 


May  24,  1919 


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AGRIC. 
LIBRARY 


HANDBOOK    OF    THE    DISEASES    OF    VEGETABLES 

OCCURRING   UNDER   MARKET,    STORAGE 

AND    TRANSIT    CONDITIONS 

By  GEORGE  K.  K.  LINK  and  MAX  W.  GARDNER.     Prepared  under 
the  direction  of  W.  A.  ORTON  and  W.  M.  SCOTT.1 

PREFACE 

This  handbook  is  designed  primarily  to  aid  the  inspectors 
of  the  Bureau  of  Markets  in  the  detection  and  identification 
of  plant  diseases  as  they  occur  in  vegetables  under  transit, 
storage,  and  market  conditions. 

The  entire  inspection  service  and  the  survey  and  study  of 
vegetable  crop  diseases  under  transit  and  market  conditions, 
were  begun  but  little  more  than  a  year  ago,  consequently 
this  handbook,  an  outgrowth  of  that  survey  and  study,  is 
necessarily  incomplete.  The  text  and  illustrations  are  the 
property  of  the  United  States  Department  of  Agriculture, 
and  are  not  to  be  used  in  any  published  form  whatsoever. 

The  description  of  the  signs,  symptoms,  or  effects  of  each 
plant  disease  is  followed  by  a  statement  of  the  geographic 
distribution  and  the  seasonal  or  climatic  relations  of  the 
disease  so  far  as  they  are  known,  since  some  diseases  occur 
only  in  certain  districts  and  often  only  under  certain  con- 
ditions. 

A  statement  is  made  as  to  the  time  and  place  of  incep- 
tion, development,  and  spread  of  the  disease.  This  is 
especially  important  from  a  market  point  of  view.  For 
example,  in  placing  the  responsibility  for  the  poor  condition 
of  a  shipment  caused  by  bacteria  or  fungi,  it  is  essential  to 
bear  in  mind  that  some  diseases  are  field  infections  and  do 
not  develop  nor  spread  in  transit  or  storage ;  that  others  are 
field  infections  which  develop  or  progress  but  do  not  spread 
ih  transit  or  storage ;  that  others  are  field  infections  which 
develop  and  spread  under  transit  and  storage  conditions; 
and  finally  that  a  number  are  transit  and  storage  infections 
of  stock  perfectly  sound  when  harvested. 

It  is  fully  realized  that  at  present  not  all  decay  can  be 
referred  to  clearly  defined  causes.  However,  by  specifying 
whenever  possible  the  disease  responsible  for  the  decay  or 
defect  in  a  consignment,  the  inspector  can  further  the  con- 


1  Dr.  V.  B.  Stewart  was  consulted  freely  in  the  preparation  of  the  text.  In  addition, 
the  following  men  were  consulted  with  reference  to  special  portions  as  enumerated 
below:  Beans,  Mr.  W.  W.  Gilbert  and  Mr.  G.  A.  Meckstroth;  cabbage  and  other  cruci- 
fers,  Dr.  L.  L.  Barter  and  Dr.  L.  O.  Kunkel;  celery,  Dr.  I.  C.  Jagger;  cucumber,  Mr. 
W.  W.  Gilbert  and  Mr.  W.  N.  Ankeney;  potato,  Dr.  H.  A.  Edson,  Prof.  L.  R.  Jones, 
Dr.  L.  O.  Kunkel,  Dr.  W.  A.  Orton,  Mr.  M.  Shapovalov,  Mr.  E.  S.  Schultz,  and  Dr. 
H.  G.  MacMillan;  onion,  Dr.  J.  C.  Walker;  lettuce,  spinach,  radish,  etc.,  Dr.  I.  C. 
Jagger,  Mr.  J.  B.  Norton  and  Mr.  L.  P.  Byars ;  tomato,  Mr.  G.  H.  Godfrey,  Mr.  F.  J. 
Pritchard,  Dr.  J.  Rosenbaum  and  Mr.  W.  B.  Clark;  watermelon,  Mr.  F.  C.  Meier;  sweet 
potato,  Dr.  L.  L.  Harter  and  Dr.  J.  L.  Weimer. 


922 


2  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

trol  and  prevention  of  diseases,  with  the  resultant  improve- 
ment of  American  agriculture  and  the  elimination  of  waste. 
Inspectors  should  make  it  a  point  to  send  in  material  con- 
cerning which  they  are  in  doubt.  By  doing  this  they  will  aid 
themselves  in  acquiring  a  better  acquaintance  with  the  vari- 
ous diseases,  and  will  aid  in  the  detection  of  new  diseases  or 
of  the  occurrence  of  diseases  in  regions  from  which  they 
have  not  been  previously  reported.  Cartons  and  franked 
tags  will  be  supplied  the  inspectors  for  use  in  sending  such 
material.  Many  specimens  can  best  be  sent  wrapped  in 
paper  (newspaper  does  admirably).  It  is  very  important 
that  material  be  mailed  without  delay. 


MARKET  DISEASES  OF  VEGETABLES. 


INTRODUCTION. 

THE   NORMAL    PLANT. 
Plants  and  Plant  Parts  Are   Living. 

T VEGETABLES  and  fruits  are  plants  or  plant  parts  and 
V  are  alive.  Few  people  realize  that  a  potato,  an  onion, 
an  apple,  or  other  fruit  or  vegetable  is  alive  and  is  therefore 
subject  to  injury,  disease,  and  death.  Failure  to  realize  this 
fact  is  responsible  for  much  of  the  loss  in  the  handling  of 
fruits  and  vegetables. 

The  Structure  of  Plants. 

Our  agricultural  plants  are  composed  of  members  or 
organs,  such  as  the  root,  stem,  leaf,  flower,  and  fruit.  These 
organs  in  turn  are  composed  of  tissues,  the  stem,  for 
example,  usually  being  composed  of  pith,  ring,  and  bark 
tissue.  Tissues,  finally,  are  made  up  of  cells,  which  are 
microscopic  in  size. 

Plant  tissues  often  are  classified  according  to  their  func- 
tions. There  are,  for  example,  the  protective  tissues,  the 
supporting  tissues,  the  conductive  tissues,  the  food-making 
tissues,  and  the  storage  tissues. 

The  Plant  Cell  and  Tissues. 

The  cell  is  the  unit  of  composition,  structure,  and  function 
of  all  plants.  It  is  composed  of  the  living  substance  proto- 
plasm, together  with  its  products  and  inclusions.  One  of 
the  products  of  the  jelly-like  protoplasm  is  the  rigid  cell 
wall  in  which  it  encases  itself  and  which  gives  shape  and 
rigidity  to  the  cell  and  to  the  tissues.  Tissues  and  cell  walls 
often  remain  intact  long  after  the  protoplasm  has  died.  In 
some  diseases,  the  cementing  substance  which  holds  adjoin- 
ing cells  together  is  dissolved  out,  and  disintegration  of  the 
tissue  results.  In  other  cases  the  cell  walls  are  punctured 
and  the  protoplasm  is  killed.  Chemical  analysis  of  plant 
tissues,  which  are,  of  course,  composed  of  cells,  yields  prin- 
cipally water,  proteins,  carbohydrates,  fats,  and  salts.  Water 
is  by  far  the  most  abundant  single  constituent,  most  plant 
tissues  containing  70-75  per  cent  water. 

The  structure  of  plant  tissues  is  roughly  comparable  to 
that  of  honeycomb  except  that  the  cells  of  plant  tissues  are 
not  as  closely  packed  as  those  of  honeycomb.  There  are 
spaces  between  plant  cells,  called  intercellular  spaces,  which 
are  most  marked  in  leafy  tissues.  These  constitute  the  ven- 
tilation system  of  the  plant,  and  through  them  the  cells  are 
in  communication  with  the  air. 

The  epidermis  or  outermost  protective  layer  of  cells  of 
leaves  and  young  stems  and  roots  has  many  minute  open- 
ings or  breathing  pores,  the  stomata.  Through  these,  water 


4  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

vapor  from  the  moist  intercellular  spaces  escapes  into  the 
air,  and  carbon  dioxide  and  oxygen  exchange  between  the 
cells  and  the  air  takes  place.  The  loss  of  water  by  the  living 
plant  through  evaporation  is  known  as  transpiration. 

When  unbroken,  the  epidermis  prevents  excessive  loss  of 
water  from  the  moist  tissues  underneath  and  keeps  out  for- 
eign organisms  such  as  fungi  and  bacteria.  In  older  stems 
and  roots,  such  as  the  Irish  potato,  the  protective  covering  is 
composed  of  cork  layers,  in  which  the  breathing  pores  are 
present  as  lenticels. 

The  supporting  tissues,  such  as  the  veins  of  leaves  or  the 
fibers  of  stems,  are  composed  of  woody  or  thickened  cells. 
The  conducting  tissues,  found  in  the  veins  of  leaves  or  the 
ring  tissues  of  stems  or  roots,  translocate  the  water  and  min- 
erals taken  in  by  the  absorptive  tissues  of  the  roots,  and  the 
food  made  in  the  food-making  tissues. 

The  green  color  of  vegetation  is  due  to  a  substance  known 
as  leafgreen  or  chlorophyll.  By  virtue  of  chlorophyll,  and 
with  the  aid  of  sunlight,  the  green  tissues  of  plants  are  able 
to  manufacture  carbohydrates  (sugars  and  starches)  from 
the  carbon  dioxide  of  the  air  and  the  water  of  the  soil. 

These  carbohydrates  are  the  basic  substances  from  which 
the  other  principal  food  of  plants  and  animals,  such  as  fats, 
oils,  and  proteins,  are  manufactured  by  green  and  non-green 
cells. 

Many  plants  possess  tissues  in  which  they  accumulate 
excess  food  materials.  These  are  the  storage  tissues.  The 
Irish  potato  and  the  sweet  potato  are  to  a  large  degree  com- 
posed of  storage  cells  in  which  starch  and  sugar,  respec- 
tively, are  stored. 

Digestion  and  Respiration. 

The  stored  food  of  the  potato  is  in  the  form  of  starch 
grains.  In  the  spring  when  the  potato  sprouts,  the  insoluble 
starch  is  changed  to  soluble  sugar,  to  which  is  due  the  sweet 
taste  of  potatoes  at  that  season.  In  ripening  plant  tissues, 
insoluble,  unpalatable  substances,  such  as  starch  and  tan- 
nins, become  soluble,  aromatic,  and  palatable. 

Another  process  which  goes  on  in  all  protoplasm,  plant  or 
animal,  is  respiration.  The  making  of  food  out  of  simple 
materials  is  a  constructive  process,  whereas  respiration  is 
destructive.  In  its  simplest  form,  it  involves  a  consumption 
of  oxygen,  a  burning  or  oxidation  of  the  substances  of  the 
cell,  such  as  sugar,  starch,  fat,  and  proteins,  and  a  liberation 
of  carbon  dioxide  gas,  water,  and  energy.  Part  of  this 
energy  is  manifested  as  heat.  The  so-called  "heating"  of 
crops  in  transit  and  storage  generally  is  due  to  the  heat 
evolved  in  respiration. 

The  rate  of  respiration  is  greatly  influenced  by  tempera- 
ture. At  high  temperatures,  respiration  proceeds  at  a  rapid 
rate,  and  the  food  substances  are  soon  burned  up.  At  low 
temperatures,  the  rate  of  respiration  is  so  retarded  that  it 


MARKET  DISEASES  OF  VEGETABLES.  5 

becomes  practically  negligible.  Proper  aeration  is  essential 
for  the  continued  life  and  respiration  of  vegetables.  The 
carbon  dioxide  liberated  must  be  removed,  and  the  neces- 
sary oxygen  must  be  supplied.  If  respiring  cells  are  not 
properly  aerated,  they  die,  a'nd  spoil. 

The  fundamental  reason  for  the  refrigeration  of  fruits 
and  vegetables  is  based  upon  the  fact  that  refrigeration 
retards  respiration  and  digestion ;  retards  not  only  the  ripen- 
ing processes  of  fruits  and  vegetables,  but  also  their  decay, 
which  is  due  to  the  activity  of  bacteria  and  fungi. 

Relation  of  the  Plant  to   Its  Environment. 

The  continued  existence  of  protoplasm  and  therefore  of 
plants  themselves  is  dependent  upon  external  factors  which 
constitute  the  environment  of  plants.  Some  of  these  are 
non-living,  such  as  moisture,  heat,  light,  and  the  air ;  others 
are  living,  such  as  other  plants,  or  animals.  The  environ- 
ment of  a  plant  may  vary  within  certain  limits  without 
injury  to  the  plant.  However,  if  these  limits  are  exceeded 
for  a  sufficient  period  of  time  the  plant  becomes  abnormal 
or  diseased  and  eventually  may  die. 

When  plants  or  plant  parts  are  shipped  and  stored  as 
fresh  food  products,  they  are  subjected  to  conditions  very 
unlike  those  prevailing  in  the  field,  and  care  must  be  exer- 
cised to  make  these  such  that  the  life  of  the  plant  or  plant 
parts  is  still  possible.  This  means  that  the  external  condi- 
tions must  be  controlled  and  kept  within  the  narrow  range 
tolerated  by  the  plant  in  question.  Each  crop  must  be 
handled  in  a  manner  suited  to  its  peculiar  requirements. 
This  will  depend  upon  the  climatic  conditions  prevailing 
during  the  growing  season  and  at  harvest;  upon  the  methods 
employed  for  culture  and  harvesting;  upon  the  presence  of 
climatic  or  mechanical  injuries;  upon  the  maturity  at  har- 
vesting; upon  the  method  of  packing  or  loading;  upon  the 
type  of  container ;  upon  the  length  of  the  transportation  and 
storage  periods;  upon  the  season,  and  upon  the  climatic 
conditions  to  which  the  crop  will  be  subjected  in  transit. 
Failure  to  provide  proper  conditions  for  plants  or  plant 
parts  in  transit  or  storage  results  in  the  loss,  annually,  of 
thousands  of  cars  of  fruits  and  vegetables.  It  may  result 
merely  in  an  inferior  product  so  far  as  appearance  and 
taste  are  concerned,  or  in  partial  or  complete  decay. 

The  Relation  of  Plant  Functions  to  Keeping  Quality. 

It  is  well  known  that  vegetables  and  fruits  shrink  in 
transit  and  storage.  Some  of  the  shrinkage  is  due  to  read- 
justment in  the  pack  or  load.  .  There  is  in  addition  to  this, 
however,  a  real  decrease  in  the  weight  and  volume  of  the 
crops  as  can  be  determined  by  weighing  and  measurement. 

Usually  there  is  a  very  considerable  shrinkage  immedi- 
ately following  the  harvesting  of  a  crop,  due  mainly  to  the 


6  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

loss  of  water  vapor  by  the  plant  through  its  stomata,-  or 
transpiration,  and  by  evaporation  from  cut  surfaces.  The 
loss  of  water  by  plant  organs  is  illustrated  very  strikingly 
by  the  phenomenon  commonly  known  as  "sweating,"  which 
is  the  result  of  condensation  of  this  water  vapor. 

The  first  result  of  excessive  water  loss  is  known  as  wilting. 
Wilting  is  especially  frequent  in  leafy  crops  with  large 
transpiring  surfaces,  such  as  celery,  lettuce,  or  spinach.  The 
compact,  heavy  crops  such  as  deciduous  and  citrus  fruits, 
potatoes,  and  onions  are  made  up  of  storage  tissues  and  are 
much  less  subject  to  water  loss  than  the  more  leafy  ones. 
They  lose  water  much  more  slowly  because  of  their  rather 
thick  protective  skin  and  fewer  stomata.  They  also  have  a 
greater  bulk  of  water  available  in  their  tissues,  and  a  larger 
volume  of  tissue  relative  to  their  transpiring  surface. 

Drying  of  the  surfaces  of  plants,  with  a  slight  wilting  of 
leafy  plants,  before  they  are  shipped  or  stored  is  advisable. 
Wet  plant  surfaces  favor  the  development  of  bacteria  and 
fungi  and,  when  stomata  are  filled  with  water,  easy  ingress 
is  provided  for  bacteria.  Many  crops  are  sweated,  cured, 
or  kiln-dried  before  they  are  put  into  storage  or  shipped, 
to  avoid  undue  shrinkage  by  loss  of  water,  and  to  dry  and 
harden  the  tissues  to  render  them  less  subject  to  attack  by 
bacteria  or  fungi  which  flourish  on  tender  tissues  under 
moist  conditions.  Continued  loss  of  water  by  plant  tissues 
soon  results  in  their  death  after  which  they  may  become  the 
prey  of  bacteria  and  fungi. 

i  Not  all  of  the  decrease  in  weight  of  fruits  and  vegetables 
in  storage  is  due  to  loss  of  water.  A  thoroughly  cured  sweet 
potato  loses  weight  and  shrinks  in  storage  even  when  stored 
in  a  very  humid  atmosphere,  especially  if  the  temperature 
is  high.  A  part  of  this  loss  is  due  to  transpiration,  the 
remainder  to  respiration.  At  low  temperatures,  the  pro- 
cesses go  on  very  slowly,  but  ultimately  lead  to  physiological 
breakdown.  In  other  words,  there  is  a  time  limit  to  the 
storage  of  all  living  plant  parts.  The  period  is  especially 
brief  in  the  case  of  succulent  crops.  Each  crop  has  its  period 
beyond  which  it  is  not  advisable  to  store  it.  For  example, 
a  Jonathan  apple  cannot  be  stored  as  long  as  a  Winesap. 

Proper  aeration  and  refrigeration  are  essential  in  storage 
places.  The  former  prevents  the  accumulation  of  water 
vapor  and  attendant  sweating,  provides  oxygen,  and  re- 
moves carbon  dioxide.  The  latter  decreases  the  rate  of 
digestion  and  respiration  in  the  plant  tissue,  thus  lowering 
the  rate  at  which  the  latter  consumes  itself.  More  impor- 
tant, however,  is  the  effect  of  these  factors  upon  the  bacteria 
and  fungi  which,  because  of  their  power  to  cause  decay,  are 
the  chief  enemies  of  stored  fruits  and  vegetables.  Bacteria 
and  fungi  cannot  attack  plants  when  the  plant  surfaces  are 
dry.  Furthermore,  at  low  temperatures  their  activity  is  so 
reduced  that  they  seldom  attack  plant  tissues. 


MARKET  DISEASES  OP  VEGETABLES.  7 

DISEASE   IN   PLANTS. 

Disease  in  plants  is  any  deviation  from  the  normal  con- 
dition of  their  functions  or  tissues.  The  majority  of  plant 
diseases  as  they  occur  in  the  market  are  localized  in  their 
effects  and  differ  therein  from  most  animal  diseases,  which 
usually  are  systemic,  and  affect  the  whole  body  because 
of  the  presence  of  a  nervous  and  a  circulatory  system.  For 
example,  the  outer  leaves  of  a  celery  plant  may  be  rotted 
severely  while  the  inner  leaves  or  heart  are  in  no  way 
injured  and  are  fit  for  food.  It  must  be  remembered,  how- 
ever, that  the  sound  part  of  a  fruit  and  vegetable  may  in 
some  cases  acquire  a  disagreeable  odor  or  flavor  from  the 
diseased  part.  At  times  even  sound  fruits  or  vegetables  are 
affected  in  taste  and  flavor  by  nearby  decaying  fruits  and 
vegetables. 

Types. 

Diseases  may  occur  in  the  growing  plant,  checking  and 
preventing  its  growth  or  its  production  of  normal  parts  or 
even  killing  it  outright.  They  may  also  occur  in  fruits  and 
vegetables  in  transit  and  storage.  We  may  therefore  distin- 
guish between  field  and  transportational  diseases,  and  shall 
attempt  to  differentiate  as  much  as  possible  between  dis- 
eases which  originate  in  the  field  and  those  which  originate 
in  transit  and  storage. 

For  example,  infection  of  sweet  potatoes  with  soft  rot  or 
peaches  with  brown  rot  may  occur  either  in  the  field,  in 
transit,  or  in  storage,  whereas  infection  of  sweet  potatoes 
with  scurf  or  peaches  with  scab  occurs  only  in  the  field. 
The  first  two  diseases,  however,  may  develop  or  progress  in 
the  field,  in  transit,  or  in  storage,  whereas  the  latter  two 
probably  do  not  develop  or  spread  in  transit  or  in  storage. 

Symptoms. 

The  signs  or  characteristics  of  a  disease  which  mark  it 
and  by  which  its  presence  is  discerned,  are  known  as  the 
symptoms  of  the  disease.  During  the  progress  of  a  disease, 
its  symptoms  may  change.  Frequently  there  are  early  and 
advanced  symptoms.  The  early  symptoms  of  watermelon 
anthracnose,  for  example,  are  raised  welts  on  the  rind, 
while  the  advanced  symptoms  are  deeply  sunken  lesions 
with  a  salmon  pink  covering  of  spores. 

Not  all  the  symptoms  of  a  disease  necessary  for  its  diag- 
nosis may  appear  on  one  specimen.  As  a  matter  of  fact, 
it  is  often  impossible  to  diagnose  a  disease  by  examining  a 
single  specimen,  and  a  correct  diagnosis  often  involves  an 
examination  of  the  whole  field  or  the  entire  lot  in  the  car 
or  in  storage.  In  a  shipment  of  celery,  for  example,  some 
plants  may  show  a  watery  rot.  This  condition  alone  may  be 
insufficient  for  a  correct  and  complete  diagnosis.  Other 
plants  in  the  same  shipment  may  show  a  white  cottony 


8  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

growth  of  mold  and  no  rot,  while  others  may  show  the  mold 
and  black  masses  of  the  fungus.  The  presence  of  all  of 
these  symptoms  in  a  package  or  car,  however,  furnish  the 
basis  for  a  correct  diagnosis  of  the  rot  as  watery  soft  rot  due 
to  Sclerotinia. 

Very  frequently  the  symptoms  of  several  diseases  appear 
on  the  same  specimen  or  in  the  same  lot.  A  single  potato 
may  show  symptoms  of  black  scurf,  black  heart,  and  Fusa- 
rium  tuber  rot  at  the  same  time.  Sometimes  the  symptoms 
of  one  disease  are  followed  immediately  by  those  of  another, 
as  in  black  heart  of  potatoes  followed  by  slimy  soft  rot. 

Diseases  Due  to  Living,  Parasitic  Agencies. 

Most  plant  diseases  are  caused  by  one  of  two  types  of 
minute  plant  life,  commonly  known  as  germs  and  molds  and 
often  referred  to  collectively  as  "microorganisms." 

Host  and  Parasite. 

The  plant  attacked  and  at  whose  expense  the  bacteria 
or  fungi  feed,  and  upon  and  in  which  they  live,  is  known  as 
the  host.  Bacteria  or  fungi  living  upon  and  at  the  expense 
of  a  living  plant  or  animal  are  known  as  parasites.  When 
these  live  upon  dead  plant  or  animal  matter  they  are  classed 
as  saprophytes.  Some  bacteria  and  fungi  are  restricted  to 
a  single  host;  others  can  attack  a  variety  of  hosts.  Diseases 
due  to  the  latter  type  of  organisms  are  more  likely  to  origi- 
nate in  transit  and  storage  than  those  due  to  the  former 
type. 

Bacteria  and  Fungi. 

Bacteria  are  exceedingly  small,  single-celled,  non-green 
plants  which  multiply  by  simple  division.  Under  proper 
conditions  of  temperature,  moisture,  and  food  supply,  bac- 
teria multiply  with  astounding  rapidity. 

Some  fungi  also  are  composed  of  single  cells,  but  most  of 
them  consist  of  many  cells  united  end  to  end  to  form  threads. 
A  single  thread  is  known  as  a  hypha  (plural  hyphae)  and 
the  mass  of  hyphae  of  a  fungus  is  known  as  the  mycelium. 
Generally  the  mycelium  grows  within  the  tissues  of  the 
host  and  is  invisible,  although  under  favorable  conditions  it 
may  also  grow  out  on  the  surface.  At  times  the  mycelium 
of  some  fungi  form  thickened,  hardened  masses  known  as 
sclerotia. 

Fungi  generally  reproduce  by  the  formation  and  libera- 
tion of  special  cells  or  groups  of  cells  called  spores.  In 
function,  these  spores  are  the  equivalent  of  the  seed  of 
higher  plants,  and  are  distributed  as  these  are,  by  man, 
animals,  wind,  and  water.  They  are,  of  course,  distributed 
very  much  more  readily  and  widely  because  they  are  so 
small  and  light.  The  spores  of  some  fungi,  such  as  "blue 
mold"  or  "bread  mold"  are  found  everywhere. 


MARKET  DISEASES  OF  VEGETABLES.  9 

Fungi  bear  their  spores  in  various  ways.  In  the  simpler 
types  the  spores  are  borne  on  the  surface  of  the  attacked 
plant  as  a  powdery  or  dusty  covering  such  as  one  sees  in 
blue  mold  (Penicillium)  and  gray  mold  (Botrytis).  Some, 
such  as  Rhizopus  nigricans,  bear  their  spores  in  special  cases 
called  sporangia,  (singular,  sporangium).  The  summer 
spores  of  many  fungi  are  known  as  conidia  (singular, 
conidium). 

In  other  fungi,  spores  are  produced  in  slimy  heaps  on 
little  pads  or  cushionlike  bodies  known  as  acervuli  (singu- 
lar, acervulus) .  These  are  especially  marked  in  the  anthrac- 
noses.  Still  other  fungi  bear  their  spores  in  special  flask- 
shaped  bodies  on  or  at  the  surface  of  the  diseased  portion 
of  the  attacked  plant.  These  appear  as  dots,  or  pimple-like 
bodies  and  are  known  as  pycnidia  (singular,  pycnidium). 
They  are  conspicuous  in  the  late  blight  spots  on  celery,  the 
fruit  rot  of  egg  plant,  the  Phoma  rot  of  tomatoes,  and  the 
black  rot  of  apples.  The  special  spore-bearing  structures 
of  fungi  are  known  as  fruiting  bodies.  The  fruiting  bodies 
which  result  from  fertilization  and  contain  the  winter  spores 
do  not  occur  generally  under  market  and  storage  conditions. 

There  are  four  classes  of  fungi,  Phycomycetes,  Ascomy- 
cetes,  Fungi  Imperfecti,  and  Basidiomycetes.  Most  of  the 
fungi  with  which  we  will  deal  belong  to  the  third  of  these 
groups. 

The  Life  Processes  of  Bacteria  and  Fungi. 

The  protoplasm  of  bacteria  and  fungi  lacks  chlorophyll 
and  therefore  cannot  manufacture  its  own  food,  but  must 
obtain  it  from  green  plants,  either  directly  or  indirectly.  It 
obtains  its  food  and  energy  by  digestive  and  respiratory 
processes  from  the  tissue  attacked.  This  digestive  and 
respiratory  action  of  bacteria  and  fungi  is  popularly  known 
as  fermentation.  Bacterial  rots  generally  are  accompanied 
by  putrefactive  odors  due  to  the  breaking  down  of  protein 
compounds. 

The  attack  upon  living  tissues  by  parasites  leads  to  a  dis- 
turbance in  the  functions,  structure,  and  composition  of  the 
attacked  plant,  in  other  words,  to  disease.  The  diseased 
areas  produced  by  parasites  or  other  causes  are  known  as 
lesions.  At  present  only  those  produced  by  the  action  of 
parasites  will  be  considered.  A  lesion  may  be  a  leaf  or 
pod-spot,  a  wart,  a  soft  or  dry-rot,  or  a  canker,  depending 
upon  the  parasite,  the  external  conditions,  and  the  nature 
and  response  of  the  affected  host  tissues.  Soft  rot  of  the 
carrot,  for  example,  consists  of  lesions  caused  by  Bacillus 
carotovorus.  These  bacteria  secrete  ferments  or  enzymes 
which  digest  or  dissolve  the  cementing  substances  between 
the  carrot  cells  and  disintegrate  the  tissue  into  a  soft,  slimy 
mass. 

In  other  diseases  the  lesions  arise  in  a  different  manner. 
In  anthracnose  of  the  cucumber,  for  example,  the  hyphae 


10  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

of  the  fungus,  Colletotrichum  lagenarium,  penetrate  the  cell 
walls  and  feed  upon  the  protoplasm.  As  a  result,  the 
affected  cells  die  and  lose  their  water,  consequently  one  of 
the  first  symptoms  of  the  disease  is  a  water-soaked  spot  on 
the  fruit.  Since  the  water  evaporates  rapidly  from  this  spot, 
it  dries  out  and  becomes  sunken.  As  more  cells  are  killed 
and  the  lesion  enlarges,  cavities  result  from  the  shrinkage 
and  rupture  of  the  killed  tissue.  In  other  diseases,  such  as 
late  blight  of  the  potato,  the  fungus  grows  between  the  cells 
and  sends  suckers  into  the  cells,  thereby  securing  its  nour- 
ishment, and  eventually  killing  the  host  protoplasm. 

The  activity  of  the  bacteria  and  fungi,  like  that  of  other 
plants,  is  greatly  influenced  by  temperature.  Low  tempera- 
tures inhibit  the  germination  and  growth  of  these  parasites, 
consequently  are  useful  in  controlling  many  diseases.  Low 
temperatures  also  retard  digestion  and  respiration  in  these 
organisms,  consequently  decrease  their  destructive  activities. 
These  facts  are  fundamental  reasons  for  the  refrigeration 
of  fruits  and  vegetables.  Control  of  the  life  processes  of 
these  organisms  by  low  temperatures  probably  is  more 
important  than  the  effect  of  refrigeration  upon  the  life 
activities  of  the  stored  fruits  or  vegetables.  Some  fungi  and 
bacteria  can  grow  well  at  moderate  temperatures  and  conse- 
quently are  very  active  even  in  iced  cars.  Scletotinia,  for 
example,  grows  well  at  moderate  temperatures  and  there- 
fore causes  a  rot  of  celery  in  iced  cars. 

Active  bacterial  and  fungous  cells  do  not  possess  the  effec- 
tive protective  tissues  of  higher  plants,  consequently  their 
protoplasm  is  very  subject  to  drying  out.  In  the  desiccated 
state  these  organisms  are  inactive  or  resting,  and  cannot 
resume  growth  or  develop  so  long  as  they  are  dry.  In  com- 
bating diseases  caused  by  parasites,  it  is  fundamentally 
important  to  recognize  the  fact  that  a  moist  environment  is 
essential  for  their  growth  and  spread.  Dried  or  slightly 
wilted  plant  tissues,  when  shipped  or  stored  in  a  well  aer- 
ated place,  are  not  attacked  readily  by  bacteria  and  fungi. 
Loading  or  storing  wet  fruits  or  vegetables  often  leads  to 
disastrous  results  because  of  the  action  of  micro-organisms. 

Inception  of  Diseases  Due  to  Bacteria  and  Fungi. 

While  bacterial  cells  and  fungous  spores  are  everywhere 
present  in  great  numbers  on  the  exposed  surfaces  of  all 
normal  uninjured  plant  parts,  the  interior  tissue  is  usually 
absolutely  sterile ;  that  is,  free  from  all  foreign  organisms. 

Before  disease  can  occur  infection  must  take  place.  By 
infection  we  mean  the  entrance  of  the  disease-producing 
organism  into  the  host  tissue  and  its  development  therein. 
Plants  are  protected  against  the  entrance  of  foreign  organ- 
isms by  their  epidermis,  by  their  cork  layers,  and  by  the 
nature  of  their  protoplasm.  Foreign  organisms  may  gain 
entrance  through  the  unbroken  skin,  or  through  natural 
openings  in  the  epidermis  such  as  stomata  and  water  pores. 


MARKET  DISEASES  OF  VEGETABLES.  11 

However  they  generally  enter  plant  tissues  through  wounds 
or  abrasions  of  the  protective  layers.  This  type  of  infection 
is  the  most  important  in  transportational  diseases.  Injured 
or  dead  areas  offer  an 'excellent  foothold  for  rot-producing 
organisms. 

Diseases  Due  to  Non-living,  Non-parasitic  Causes. 

A  very  considerable  number  of  plant  diseases  are  due  not 
to  parasitic  organisms  but  to  other  unfavorable  factors  in 
the  environment  of  the  plants.  Water  core  and  Jonathan 
spot  of  apples,  black  heart,  hollow  heart,  and  sunburn  of 
potatoes,  tip-burn  of  lettuce  and  other  crops,  and  scald  and 
freezing  or  chilling  injury  of  vegetables  and  fruits  are  excel- 
lent examples  of  disease  due  to  non-parasitic  causes. 

Tip-burn  of  lettuce  and  other  plants,  water  core  and 
Jonathan  spot  of  apples,  and  blossom-end  rot  of  tomatoes 
and  watermelons  probably  are  due  to  irregularities  in  the 
water  relations  of  these  crops.  The  nature  of  the  plants 
themselves  is  also  a  very  important  factor  in  such  troubles. 
For  example,  with  the  same  soil  and  climatic  conditions,  the 
same  water  supply,  and  the  same  treatment  of  trees  of  vari- 
ous varieties,  the  Jonathan  and  the  'Grimes  Golden  alone 
may  show  Jonathan  spot.  Black  heart  of  potatoes  is  a  good 
example  of  the  evil  effects  of  disturbed  respiration  in  plants. 

Under  normal  conditions,  oxygen  enters  the  internal 
tissues  of  the  potato  at  a  rate  sufficiently  rapid  to  maintain 
normal  respiration.  However,  if  the  temperature  is  raised 
to  100°  F.,  the  rate  of  respiration  is  so  increased  that  oxygen 
cannot  penetrate  to  the  inner  cells  rapidly  enough  to  supply 
their  needs.  As  a  result  the  internal  tissues  of  the  tuber 
become  asphyxiated,  die,  and  turn  black. 

If  potatoes  are  kept  at  normal  temperatures  but  are  not 
well  aerated  and  do  not  have  a  normal  supply  of  oxygen, 
black  heart  also  results.  In  this  case  the  death  and  dis- 
coloration of  the  cells  is  not  restricted  to  the  heart  of  the 
potato. 

Chilling  and  freezing  injury  are  good  examples  of  the 
effects  of  excessively  low  temperature  upon  plant  tissues, 
while  sunscald  is  an  example  of  the  effect  of  extremely  high 
temperature.  Either  extreme  kills  the  tissues. 

Tolerance,  Resistance  and  Predisposition  to  Disease. 

Many  plants  have  to  a  certain  degree  an  ability  to  tolerate 
unfavorable  climatic,  soil,  and  cultural  conditions,  and  to 
withstand  or  tolerate  the  attacks  of  bacteria  and  fungi. 
This  tolerance  varies  with  the  age  and  variety  of  the  plant 
and  with  the  conditions  under  which  the  plant  is  grown. 

Resistance  to  parasitic  attack  may  be  due  to  the  nature 
and  thickness  of  the  protective  covering  of  the  plant,  to  a 
scarcity  of  natural  openings,  to  the  rapidity  with  which 
wounds  heal  over  (with  wound  cork),  to  the  time  of  ma- 


12         .  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

turity  of  the  plant,  to  the  acidity  of  its  tissues,  or  more 
commonly  to  some  unknown  factor  in  the  composition  of  the 
protoplasm  of  the  cells  themselves.  * 

Disease   Control. 

By  disease  control  is  meant  the  elimination,  the  checking, 
or  the  prevention  of  a  disease.  Plant  diseases  usually  are 
controlled  by  prevention  rather  than  cure.  A  very  gener- 
ally used  method  in  the  control  of  diseases  due  to  parasites 
is  the  spraying,  dusting,  or  dipping  of  plants  or  plant  parts 
to  kill  the  fungi  and  bacteria  present  on  the  surfaces,  or  to 
prevent  the  germination  of  spores  that  may  lodge  thereon 
subsequently.  There  are  a  number  of  other  practical 
methods  of  disease  control,  such  as  proper  cultural  methods, 
crop  rotation,  soil  and  seed  sanitation,  planting  of  disease- 
free  stock  or  disease-resistant  varieties,  and  the  variation 
of  the  planting  date. 

In  the  control  of  transportational  diseases,  icing,  refrig- 
eration, ventilation,  precaution  not  to  pack  wet  plants  or 
plant  organs,  drying  of  plants,  and  careful  handling  are 
important  means  of  disease  control. 


MARKET  DISEASES  OF  VEGETABLES.  13 


LITERATURE    CITED. 

In  addition  to  these  special  references,  the  following  books  will  be 
found  very  helpful  and  should  be  freely  consulted : 

Freeman,  E.  M.     Minnesota  plant  diseases.     1905. 

Duggar,  B.  M.    Fungous  diseases  of  plants.     1909. 

Stevens,  F.  L.,  and  Hall,  J.  G.     Diseases  of  economic  plants.     1910. 

Hesler,  L.  R.,  and  Whetzel,  H.  H.     Manual  of  fruit  diseases.     1917. 

Coons,  G.  H.,  and  Nelson,  R.  The  plant  diseases  of  importance  in  the 
transportation  of  fruits  and  vegetables.  Am.  Ry.  Perishable  Freight 
Assn.  Cir.  473-A.  1918. 

(1)  Bartholomew,  E.  T. 

1913.  Black  heart  of  potatoes.     In  Phytopathology,  v.  3,  No.  3, 

p.  180-182,  pi.  19. 

(la)Bessey,  E.  A.,  and  Byars,  L.  P. 

1915.  The  control  of  root-knot.  U.  S.  Dept.  Agr.  Farmers'  Bui. 
648,  19  p. 

(2)  Brandes,  E.  W. 

1918.  Anthracnose  of  lettuce  caused  by  Marssonina  panattoni- 
ana.  In  Jour.  Agr.  Research,  v.  13,  No.  5,  p.  261-280, 
4  fig.,  pi.  C,  20.  Literature  cited,  p.  280. 

(3)  Brooks,  Charles. 

1914.  Blossom-end  rot  of  tomatoes.     In  Phytopathology,  v.  4, 

No.   5,  p.   345-374,  4  fig.,  pi.   24-26.      References,  p. 
372-373. 

(4)  Brown,  Nellie  A. 

1915.  A  bacterial  disease  of  lettuce.*     A  preliminary  report. 

In  Jour.  Agr.  Research,  v.  4,  No.  5,  p.  475-478.   Litera- 
ture cited,  p.  478. 

(5)  Burger,  O.  F. 

1913.  Lettuce  drop.     Fla.  Agr.  Exp.  Sta.   Bui.   116,  p.  27-32, 

illus. 

(6)   

1914.  Cucumber  rot.     Fla.  Agr.  Exp.  Sta.  Bui.  121,  p.  97-109, 

fig.  37-42. 

(7)  Carpenter,  C.  W. 

1915.  Some  potato  tuber-rots  caused  by  species  of  Fusarium. 

Jour.  Agr.  Research,  v.  5,  No.  5,  p.  183-210,  pi.  A-B, 
14-19. 

(8)  Carsner,  Eubanks. 

1918.  Angular-leafspot  of  cucumber:  dissemination,  overwin- 
tering and  control.  In  Jour.  Agr.  Research,  v.  15,  No. 
3,  p.  201-220,  pi.  13-16.  Literature  cited,  p.  220. 

(9)  Chittenden,  F.  H.,  and  Orton,  W.  A. 

1918.  How  to  increase  the  potato  crop  by  spraying.  U.  S.  Dept. 
Agr.  Farmers'  Bui.  868,  p.  13-16. 

(10)  Cook,  M.  T.,  and  Lint,  H.  C. 

1915.  Potato  diseases  in  New  Jersey.   N.  J.  Agr.  Exp.  Sta.  Circ. 

53,  23  p.,  9  fig.     Substitute  for  Circ.  33,  now  out  of 
print. 

(11)  Coons,  G.  H..  and  Levin,  Ezra. 

1916.  The  Septoria  leaf  spot  disease  of  celery,  or  celery  blight. 

Mich.  Agr.  Exp.  Sta.  Spec.  Bui.  77,  8  p.,  9  fig. 

*  Papers  marked  with  a  star  are  exhausted  so  far  as  the  Department  supply  is 
concerned.  Copies  may  be  purchased  from  the  Superintendent  of  Documents,  Govern- 
ment Printing  Office,  Washington,  D.  C. 


14  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

(12)  Doolittle,  S.  P. 

1916.  Cucumber  scab  caused  by  Cladosporium  cucumerinum. 
In  17th  Rpt.  Mich.  Agr.  Acad.  Sci.  [1915]:  87-116. 
Literature,  p.  116. 

(13)   

1916.  A  new  infectious  mosiac  disease  of  cucumber.  In  Phyto- 
pathology, v.  6,  No.  2,  p.  145-147. 

(14)  Edgerton,  C.  W. 

1910.  The  bean  anthracnose.  La.  Agr.  Exp.  Sta.  Bui.  119,  55 
p.,  14  pi.  Bibliography,  p.  51-54. 

(15)   and  Moreland,  C.  C. 

1913.  The  bean  blight  and  preservation  and  treatment  of  bean 

seed.     La.  Agr.  Exp.  Sta.  Bui.  139,  43  p.,  6  pi. 

(16)  Edson,  H.  A. 

1915.   Rheosporangium    aphanidermatum,    a    new    genus    and 
species  of  fungus  parasitic  on  sugar  beets  and  radishes. 
In  Jour.   Agr.   Research,  v.   4,  No.   4,  p.  279-292,  pi. 
44-48. 
(17) 

1915.  Seedling  diseases  of  sugar  beets  and  their  relation  to 

root-rot  and  crown-rot.  In  Jour.  Agr.  Research,  v.  4, 
No.  2,  p.  135-168,  pi.  16-26.  Literature  cited,  p. 
165-168. 

(18)  Erwin,  A.  T. 

1916.  Late  potato  blight  in  Iowa.     Iowa  Agr.  Exp.  Sta.   Bui. 

163,  p.  287-305,  8  fig. 

(19)  Galloway,  B.  T. 

1895.  The  growth  of  lettuce  as  affected  by  the  physical  proper- 
ties of  the  soil.  In  Agr.  Sci.,  v.  8,  p.  302-316. 

(20)   

1895.   Commercial  lettuce  forcing.  In  Amer.  Gard.,  v.  16,  p.  135. 

(21)  Gardner,  M.  W. 

1918.  Anthracnose  of  cucurbits.  U.  S.  Dept.  Agr.  Bui.  727, 
68  p. 

(22)  Gilbert,  W.  W. 

1916.  Cucumber  mosaic  disease.  In  Phytopathology,  v.  6,  No. 
2,  p.  143-144,  pi.  5. 

(23)  Harter,  L.  L. 

1914.  Fruit-rot,    leaf -spot,    and    stem-blight    of    the    eggplant 

caused  by"  Phomopsis  vexans.  In  Jour.  Agr.  Research, 
v.  2,  No.  55,  p.  331-338,  1  fig.,  pi.  26-30. 

(24)   

1916.  Sweet  potato  diseases.     U.  S.  Dept.  Agr.  Farmers'  Bui. 

714,  26  p.,  21  fig. 

(25) 

1917.  Podblight  of  the  lima  bean  caused  by  Diaporthe  phaseo- 

lorum.  In  Jour.  Agr.  Research,  v.  11,  No.  10,  p.  474- 
504,  11  fig.,  pi.  42-43.  Literature  cited,  p.  502-504. 

(26)   and  Jones,  L.  R. 

1918.  Cabbage  diseases.     U.  S.  Dept.  Agr.  Farmers'  Bui.  925, 

30  p.,  13  fig. 

(27) ,  Weimer,  J.  L.,  and  Adams,  J.  M.  R. 

1918.  Sweet  potato  storage  rots.  In  Jour.  Agr.  Research,  v. 
15,  No.  6,  p.  337-368. 

(28)  Hawkins,  L.  A. 

1916.  The  disease  of  potatoes  known  as  "leak."*     In  Jour.  Agr. 

Research,  v.  6,  No.  17,  p.  627-640,  1  fig.,  pi.  90. 

(29)    

1917.  Experiments  in  the  control  of  potato  leak.     U.  S.  Dept. 

Agr.  Bui.  577,  5  p. 


MARKET  DISEASES  OF  VEGETABLES.,  15 

(30)  Humbert,  J.  G. 

1918.  Tomato  diseases  in  Ohio.  Ohio  Agr.  Exp.  Sta.  Bui  321 
p.  157-196,  illus. 

(31)  Jagger,  I.  C. 

1916.  Experiments  with  the  cucumber  mosaic  disease.     In  Phy- 

topathology, v.  6,  No.  2,  p.  148-151. 

(32)  Jamieson,  Clara  O. 

1915.  Phoma  destructiva,  the  cause  of  a  fruit  rot  of  the 
tomato.*  In  Jour.  Agr.  Research,  v.  4,  No.  1,  p.  1-20, 
pi.  1-6  (2  col.).  Literature  cited,  p.  19-20. 

(33)  Jones,  L.  R. 

1901.  A  soft  rot  of  carrot  and  other  vegetables.     In  Vt.  Agr. 
Exp.  Sta.  13th  Ann.  Rpt.  1899-1900,  p.  299-332,  illus. 
(33a)  Jones,  L.  R.,  and  Bailey,  Ernest. 

1917.  P'rost  necrosis  of  potato  tubers.     In  Phytopathology,  v.  7, 

No.  1,  p.  71-72. 

(34)  .         _,  Giddings,  N.  J.,  and  Lutman,  B.  F. 

1912.  Investigations  of  the  potato  fungus  Phytophthora  in- 
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100  p.,  illus.,  10  pi.  (2  col.),  map. 

(35)  Kunkel,  L.  O. 

1919.  Wart  of  potatoes;  a  disease  new  to  the  United  States. 
U.  S.  Dept.  Agr.  Bur.  Plant  Indus.  Office  Cotton, 
Truck,  and  Forage  Crop  Diseases,  Circ.  6. 

(36)  Levin,  Ezra. 

1917.  Control  of  lettuce  rot.     In  Phytopathology,  v.  7,  No.  5,  p. 

392-393. 

(37)  Link,  G.  K.  K. 

1916.  A  physiological  study  of  two  strains  of  Fusarium  in  their 
causal  relation  to  tuber  rot  and  wilt  of  potato.  Nebr. 
Agr.  Exp.  Sta.  Research  Bui.  9,  45  p.,  illus. 

(38)  Lutman,  B.  F. 

1913.  The  pathological  anatomy  of  potata  scab.     In  Phytopath- 

ology, v.   3,  No.   5,   p.    255-264,   illus.      Bibliography, 
p.  264. 

(39)   and  Cunningham,  G.  C. 

1914.  Potato  scab.     Vt.  Agr.  Exp.  Sta.  Bui.  184,  64  p.,  6  fig., 

12  pi.     Bibliography,  p.  62-64. 

(40)  McKay,  M.  B.,  and  Pool,  Venus  W. 

1918.  Field    studies    of    Cercospora    beticola.      In    Phytopath- 

ology, v.  8,  No.  3,  p.  119-136,  illus. 

(41)  MacMillan,  H.  G. 

191 8.  Sun-scald  of  beans.  In  Jour.  Agr.  Research,  v.  13,  No. 
12,  p.  647-650,  pi.  64-66. 

(42)  Meier,  F.  C. 

1916.  Watermelon  stem-end  rot.  [Preliminary  report.]  In 
Jour.  Agr,  Research,  v.  6,  No.  4,  p.  149-152,  pi.  17. 

(43)  Melhus,  I.  E. 

1913.  Silver  scurf,  a  disease  of  the  potato. f     In  U.   S.  Dept. 

Agr.  Bur.  Plant  Indus.  Circ.  127,  p.  15-24,4  fig.    Biblio- 
graphy, p.  24. 

(44)    

1914.  Powdery  scab   ('Spongospora  subterranea)   of  potatoes.f 

U.  S.  Dept.  Agr.  Bui.  82,  16  p.,  3  pi.     Bibliography, 
p.  15-16. 

(45)  - 

1915.  Hibernation    of    Phytophthora    infestans    in    the    Irish 

potato.*   In  Jour.  Agr.  Research,  v.  5,  No.  2,  p.  7.1-102, 
3  fig.,  pi.  4-8.     Literature  cited,  p.  100-102. 


t  Papers  marked  with  a  dagger  are  out  of  print. 


16  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

(46)  Morse,  W.  J. 

1914.  Powdery  scab  of  potatoes.  Maine  Agr.  Exp.  Sta.  Bui. 
227,  p.  87-104,  fig.  44-52. 

(47)  Muncie,  J.  H. 

1914.  Two  Michigan  bean  diseases.     Mich.  Agr.  Exp.  Sta.  Spec. 

Bui.  68,  12  p.,  2  fig.,  1  pi.   (col.). 

(48)  Munn,  M.  T. 

1917.  Neck-rot  disease  of  onions.  N.  Y.  State  Agr.  Exp.  Sta. 
Bui.  437,  p.  361-455,  11  pi.  Bibliography,  p.  450-455. 

(49)  Orton,  C.  R. 

1916.  The  diseases  of  the  potato.     Penn.  Agr.  Exp.  Sta    Bui. 

140,  37  p.,  23  fig. 

(50)  Orton,  W.  A. 

1913.  Potato  tuber  diseases.'  U.  S.  Dept.  Agr.  Farmers'  Bui. 
544,  16  p.,  illus. 

(51)  — 

1917.  Watermelon  diseases.     U.   S.   Dept.   Agr.   Farmers'  Bui. 

821,  18  p.,  11  fig. 

(52)  Osmun,  A.  V.,  and  Anderson,  P.  T. 

1915.  Ring-spot  of  cauliflower.     In  Phytopathology,  v.  5,  No.  5, 

p.  260-265,  4  fig.  Literature  cited,  p.  265. 

(53)  Pratt,  O.  A. 

1916.  Control    of    the    powdery    dryrot    of    western    potatoes 

caused  by  Fusarium  trichothecioides.*     In  Jour.  Agr. 
Research,  v.  6,  No.  21,  p.  817-831,  pi.  108. 

(54)   

1916.  A  western  field-rot  of  the  Irish  potato  tuber  caused  by 
Fusarium  radicicola.  In  Jour.  Agr.  Research,  v.  6, 
No.  9,  p.  297-310,  pi.  34-37. 

(55)  Rogers,  S.  S. 

1911.  The  late  blight  of  celery.     Calif.  Agr.  Exp.  Sta.  Bui.  208, 

p.  83-115,  illus.,  1  pi. 

(56)  Rosenbaum,  Joseph 

1918.  The  origin  and  spread  of  tomato  fruit  rots  in  transit. 

In   Phytopathology,   v.    8,   No.    11,   p.    572-580,   illus., 
pi.  4. 

(57)  Schultz,  E.  S. 

1916.  Silver-scurf  of  the  Irish  potato  caused  by  Spondylocla- 

dium  atrovirens.*     In  Jour.  Agr.  Research,  v.  6,  No. 
10,  p.  339-350,  pi.  45-48.     Literature  cited,  p.  350. 

(58)  Sheldon,  J.  L. 

1904.  Diseases  of  melons  and  cucumbers  during  1903  and  1904. 
W.  Va.  Agr.  Exp.  Sta.  Bui.  94,  p.  119-138,  pi.  1-5. 

(59)  Sherbakoff,  C.  D. 

1917.  Buckeye  rot  of  tomato  fruit.     In  Phytopathology,  v.  7, 

No.  2,  p.  119-129,  5  fig. 

(60)   

1917.  Some  important  diseases  of  truck  crops  in  Florida.  Fla. 
Agr.  Exp.  Sta.  Bui.  139,  p.  191-277,  fig.  76-112. 

(61)  Smith,  Erwin  F. 

1911-14.  Bacteria  in  Relation  to  Plant  Diseases,  v.  2,  1911; 
v.  3,  1914.  Washington,  D.  C.  (Carnegie  Inst.  Wash- 
ington Pub.  27,  v.  2-3. ) 

(62)  —     — ,  and  Bryan,  Mary  K. 

1915.  Angular  leaf -spot  of  cucumbers.*  In  Jour.  Agr.  Re- 
search, v.  5,  No.  11,  p.  465-476,  pi.  43-49. 

(63)  Spaulding,  Perley,  and  Field,  Ethel  C. 

1912.  Two  dangerous  imported  plant  diseases. f     U.   S.   Dept. 

Agr.  Farmers'  Bui.  489,  29  p.,  3  fig. 

(64)  Stakman,  E.  C.,  and  Tolaas,  A.  G. 

1912.  Potato  diseases.  Minn.  Agr.  Exp.  Sta.  Ext.  Bui.  35,  15 
p.,  7  fig. 


MARKET  DISEASES  OF  VEGETABLES.  17 

(65)  Stevens,  F.  L. 

1911.  A  serious  lettuce  disease  (lettuce  sclerotiniose).  N.  C. 
Agr.  Exp.  Sta.  Bui.  217,  p.  7-21,  illus. 

(66)    ,  and  Hall,  J.  G. 

1911.  A  serious  lettuce  disease  (sclerotiniose)  and  a  method 
of  control.  N.  C.  Agr.  Exp.  Sta.  Tech.  Bui.  8,  p.  89- 
143.  Bibliography,  p.  144. 

(67)  Stewart,  F.  C. 

1899.  Notes  on  various  plant  diseases.  I.  A  bacterial  rot  of 
onions.  In  N.  Y.  State  Agr.  Exp.  Sta.  Bui.  164,  p. 
209-212,  pi.  1-2. 

(68)    ,  and  Mix,  A.  J. 

1917.  Blackheart    and    the    aeration    of    potatoes    in    storage. 

N.  Y.  Agr.  Exp.  Sta.  Bui.  436,  p.  319-362,  10  pi. 

(69)  Taubenhaus,  J.  J. 

1918.  Pox,  or  pit  (soil  rot),  of  the  sweet  potato.     In  Jour.  Agr. 

Research,  v.  13,  No.  9,  p.  437-450,  pi.  51-52.     Litera- 
ture cited,  p.  449-450. 

(70)  -         — ,  and  Manns,  T.  F. 

1915.  The  diseases  of  the  sweet  potato  and  their  control.     Del. 

Agr.  Exp.  Sta.  Bui.  109,  55  p.,  65  fig.     Literature  on 
potato  diseases,  p.  48-51. 

(71)  Thaxter,  Roland. 

1890.  The  "smut"  of  onions.  Conn.  Agr.  Exp.  Sta.  Ann.  Rpt. 
1889,  p.  129-154,  pi.  1-3. 

(72)  — 

1890.   The  onion  Vermicularia  (Vermicularia  circinans).     Conn. 

Agr.  Exp.  Sta.  Ann;  Rpt.  1889,  p.  163-165. 
(72a)Tisdale,  W.  H. 

1916.  A  Melanconium  parasitic  on  the  tomato.     In  Phytopath- 

ology, v.  6,  p.  390-394. 

(73)  Van  Hook,  J.  M. 

1906.  Blighting  of  field  and  garden  peas,  chiefly  due  to  seed 
infection.  Ohio  Agr.  Exp.  Sta.  Bui.  173,  p.  229-249, 
12  fig. 

(74)  Van  Pelt,  Wayne. 

1917.  Black  mold  of  onions.     Ohio  Agr.  Exp.  Sta.  Mo.  Bui.,  v. 

2,  No.  5,  p.  152-156,  illus. 

(75)  Whetzel,  H.  H. 

>906.  Some  diseases  of  beans.  N.  Y.  Cornell  Agr.  Exp.  Sta. 
Bui.  239,  p.  195-214,  illus. 

(76)   

1908.  Bean  anthracnose.  N.  Y.  Cornell  Agr.  Exp.  Sta.  Bui. 
255,  p.  429-447,  fig.  217-222. 


18  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

GRAY    MOLD    ROT 

OF  ARTICHOKE,  BEET,  CABBAGE,  CARROT,  CAULIFLOWER,  CITRON,  LET- 
TUCE,  ONION,  PARSNIP,  RHUBARB,  RUTABAGA,  SALSIFY,  SHALLOTS, 
TURNIP,  AND  OTHER  VEGETABLES. 

Cause :    A  fungus  (Botrytis) . 

This  is  a  semi-watery  to  watery  soft  rot  characterized 
externally  by  a  gray  velvety  fungous  growth.  Frequently 
there  is  a  slight  tinge  of  green  or  brown  in  the  gray  color  of 
this  mold.  At  times  gray  to  black  solid  masses  known  as 
sclerotia  are  produced  on  the  affected  tissues  as  in  the  case 
of  the  gray  mold  rot  of  onions  generally  known  as  "neck 
rot." 

Gray  mold  rot  can  be  differentiated  from  the  watery  soft 
rot  caused  by  Sclerotinia  by  the  gray  color  of  the  mold  and 
by  the  absence  of  a  cottony  mycelium. 

Gray  mold  rot  can  be  differentiated  from  slimy  soft  rot 
by  the  gray  fungous  growth  and  by  the  absence  of  offensive 
odors.  Rhizopus  rot  can  be  differentiated  from  gray  mold 
rot  by  its  abundant  stringy  and  coarse  mycelium,  its  spo- 
rangia, and  its  sour  odor. 

In  case  of  doubt  as  to  the  identity  of  a  given  rot,  it  is 
advisable  to  collect  and  incubate  some  material  in  a  warm 
damp-chamber  secured  either  by  wrapping  it  in  paper  or 
by  placing  it  in  covered  pans.  If  a  mycelium  develops 
within  24  hours,  the  rot  is  not  slimy  soft  rot.  If  a  white 
cottony  mycelium  develops  which  later  becomes  matted,  the 
fungus  is  probably  Sclerotinia.  A  grayish,  powdery  fungous 
growth  indicates  Botrytis,  and  a  stringy  mycelium  with 
sporangia,  Rhizopus.  The  presence  of  sclerotia  will  further 
indicate  either  Sclerotinia  or  Botrytis. 

Often  the  watery  soft  rot  due  to  Sclerotinia  and  the  gray 
mold  rot  due  to  Botrytis  occur  either  together  or^in  close 
succession  on  the  same  specimen. 

Gray  mold  rot  does  not  progress  as  rapidly  as  watery 
soft  rot  and,  like  slimy  soft  rot,  may  be  checked  by  drying 
affected  tissues,  while  watery  soft  rot  (due  to  Sclerotinia) 
progresses  rapidly  even  under  dry  atmospheric  conditions. 

Infection  takes  place  in  the  field,  in  transit,  and  in  storage 
since  the  spores  of  the  fungus  seem  to  be  everywhere  pres- 
ent. The  fungus  may  develop  in  the  field  if  moist  weather 
prevails. 

The  rot  occurs  commonly  in  mature  tissues  kept  in  a  very 
humid  atmosphere.  It  attacks  frozen  or  bruised  tissues  very 
readily. 

Affected  stock  may  be  made  marketable  if  trimmed  and 
kept  in  a  dry,  well-ventilated  place.  It  is  not  safe  to  store 
affected  stock  because  it  is  a  menace  to  healthy  stock,  the 
fungus  spreading  readily  from  affected  to  healthy  tissues. 

Little  is  known  about  the  control  of  this  rot,  but  soil 
aeration  and  proper  ventilation  in  transit  and  storage  are 
preventive  measures.  The  neck  rot  type  of  this  rot  found 


MARKET  DISEASES  OF  VEGETABLES.  19 

on  onion  bulbs  can  be  checked  by  rapid  curing  of  the  onions 
as  soon  as  they  are  dug. 
Ref.  (48).* 

RHIZOPUS    ROT. 

OF    BEAN,     BEET,    CABBAGE,    CARROT,    ONION,     SQUASH,     SWEET    POTATO, 
TOMATO,  AND  OTHER  VEGETABLES. 

Cause:    A  fungus  (Rhizopus). 

In  its  early  stages,  Rhizopus  rot  consists  of  soft,  water- 
soaked  areas.  These  enlarge  rapidly  and  often  lead  to  a 
leaky  condition  of  affected  stock.  Under  proper  moisture 
conditions,  there  is  produced  a  coarse,  white,  stringy  mycel- 
ium bearing  white,  glistening  heads  or  sporangia,  which 
later  turn  brown  or  black.  This  mycelium  is  often  called 
"whiskers"  because  of  the  long,  loose  growth  of  hyphae. 

Generally  the  rot  is  accompanied  by  a  sour,  acid  odor, 
noticeable  when  the  diseased  tissue  is  freshly  broken.  In 
carrots,  sweet  potatoes,  and  other  crops  which  are  rich  in 
starches  and  sugars,  acetic  acid  is  produced,  giving  rise  to 
a  vinegar-like  odor.  In  cabbage  lactic  acid  is  produced  and 
an  odor  of  sauer  kraut  is  the  result. 

This  rot  is  distinguishable  from  watery  soft  rot  by  its  sour 
odor  and  by  the  presence  of  the  fluffy,  stringy  mycelium 
with  its  sporangia.  The  mycelium  of  Sclerotinia  is  white 
and  cottony  or  matted.  In  advanced  stages,  the  Rhizopus 
mycelium  collapses,  becomes  matted,  and  appears  gray  or 
brown,  but  lacks  the  black  sclerotia  of  Sclerotinia. 

The  sporangia,  the  color  of  the  mycelium,  and  the  sour 
odor  of  the  rot  distinguish  it  from  gray  mold  rot,  and  the 
presence  of  the  mycelium  distinguishes  it  from  slimy  soft  rot. 

Rhizopus  rot  is  favored  by  high  temperatures.  In  this 
respect  it  differs  from  watery  soft  rot  or  gray  mold  rot, 
both  of  which  develop  best  at  moderate  temperatures.  It 
is  common  in  overheated,  humid  cars,  especially  in  the  sum- 
mer, or  in  refrigerated  cars  in  which  the  ice  was  allowed 
to  run  low. 

Usually  the  fungus  gains  entry  through  wounds.  The 
original  infections  may  take  place  in  the  field,  in  transit,  or 
in  storage  since  the  spores  of  the  fungus  seem  to  be  every- 
where present.  The  rot  develops  and  spreads  very  rapidly. 
Like  Sclerotinia,  Rhizopus  spreads  from  affected  to  healthy 
stock  by  contact. 

Sorting  out  of  bruised  stock,  drying  of  moist  surfaces, 
and  proper  ventilation  and  refrigeration  will  act  as  effec- 
tive control  measures  in  transit  and  storage. 

SLIMY    SOFT    ROT. 

OF  BEAN,  BEET,  CABBAGE,  CARROT,  CELERY,  LETTUCE,  MUSTARD,  ONION, 
POTATO,  RADISH,  RUTABAGA,  SHALLOTS,  SPINACH,  TURNIP,  AND  OTHER 
VEGETABLES. 

Cause:  Bacteria  (Bacillus  carotovorus  group  and  other 
bacteria). 

*Reference  is  made  by  number  to  "Literature  cited,"  pp.  13-17. 


20  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

This  disease  is  a  soft  rot  characterized  by  a  slimy,  slippery 
condition  of  the  affected  tissues,  by  a  foul  odor,  and  by  the 
absence  of  fungous  growth.  The  last  characteristic  differ- 
entiates it  from  rots  caused  by  fungi.  Green,  leafy  tissues 
affected  with  slimy  soft  rot  have  a  very  dark  green  color  at 
first  much  like  hashed  spinach  but  later  become  brown  and 
black.  Light  colored  tissues,  such  as  cabbage  and  celery, 
become  yellowish  and  finally  brown. 

Slimy  soft  rot  is  differentiated  from  gray  mold  rot  by  the 
absence  of  the  powdery,  gray  growth  of  mold  and  of  the 
gray  to  black  sclerotia  characteristic  of  gray  mold  rot.  The 
offensive  odor  of  slimy  soft  rot  distinguishes  it  from  the  rot 
due  to  Rhizopus,  which  has  an  acid  odor.  Tissues  affected 
with  slimy  soft  rot  do  not  leak  as  do  tissues  affected  with 
watery  soft  rot,  but  become  a  mass  of  slime  if  kept  in  a 
moist  place.  Watery  soft  rot  progresses  even  in  a  dry 
atmosphere  after  once  well  started,  whije  the  progress  of 
slimy  soft  rot  is  arrested  by  drying  of  the  tissues. 

The  rot  proceeds  from  any  part  of  the  plant,  and  tissues 
are  predisposed  to  it  by  bruising,  chilling,  freezing,  tip-burn, 
sun-scald  or  aging.  In  the  case  of  the  southern  bunch  crops, 
only  the  leaves  are  affected.  It  is  prevalent  in  root  crops 
whenever  tissues  have  been  killed  by  exposure  to  extremely 
wet  conditions,  by  extremely  high  temperatures,  or  by  freez- 
ing. During  rainy  seasons,  slimy  soft  rot  may  ruin  southern 
potatoes  if  they  are  not  dug  at  once  and  dried.  Future  inves- 
tigations may  show  that  the  slimy  soft  rot  of  the  leafy  parts, 
and  the  soft  mushy  rot  of  the  root  or  stem  parts  of  plants, 
well  marked  in  carrots  and  cabbage,  are  not  caused  by  the 
same  organism.  The  rot  of  the  latter  sometimes  is  called 
the  "true  soft  rot."  In  carrots  that  have  been  in  storage, 
soft  rot  is  often  found,  the  central  tissue  of  the  root  being 
most  readily  attacked.  In  the  north,  soft  rot  is  common  in 
cabbage  in  the  field  late  in  the  fall,  especially  where  many 
plants  have  been  weakened  or  killed  by  the  soil  disease 
known  as  cabbage  yellows.  Such  rotted  heads  in  the  field 
are  a  source  of  danger  to  sound  stock  since  infection  may  be 
carried  on  the  knives  used  in  cutting  off  the  heads.  This 
may  account  for  the  common  occurrence  of  the  so-called 
"stump  rot"  in  cabbage  in  storage  or  transit. 

Slimy  soft  rot  occurs  commonly  in  southern  winter-grown 
bunch  crops.  It  results  from  infection  in  the  field,  in  transit 
or  in  storage,  and  develops  and  spreads  under  any  of  these 
conditions.  It  is  favored  by  the  moist  atmosphere  prevail- 
ing in  iced  barrels,  crates,  and  hampers  in  which  these  crops 
are  shipped,  and  in  the  cellars  and  pits  in  which  northern 
stock,  especially  cabbage  and  celery  and  the  root  crops,  are 
stored.  High  temperatures  are  of  even  greater  importance, 
however,  and  greatly  accelerate  the  progress  of  this  rot, 
especially  in  potatoes. 


MARKET  DISEASES  OF  VEGETABLES.  21 

Affected  stock  generally  is  not  marketable,  although 
affected  tissues  can  be  trimmed  away,  leaving  the  sound 
remainder  salable. 

The  rot  can  be  controlled  by  guarding  against  sun-scald, 
freezing  injury,  and  excessive  bruising,  by  drying  the  sur- 
faces of  vegetables,  especially  those  cut  and  bruised,  and  by 
maintaining  dry  and  cool  conditions  in  transit  and  storage. 

Ref.  Carrot  and  other  vegetables  (33)  ;  cabbage  (26)  ; 
lettuce  (4),  (36);  onion  (67). 

WATERY    SOFT    ROT. 

OF  ASPARAGUS,  BEAN,  BEET,  CABBAGE,  CARROT,  CAULIFLOWER,  CELERY, 
LETTUCE,  KOHL-RABI,  PEPPER,  SALSIFY,  SHALLOTS,  SQUASH,  TURNIP, 
AND  RUTABAGA. 

Cause:    A  fungus  (Sclerotinia). 

This  disease  is  a  watery  soft  rot  of  the  affected  tissue 
characterized  by  a  white,  cottony,  at  times  matted,  mycel- 
ium; by  the  presence  of  hard  masses  or  knots  (sclerotia) 
which  are  white  at  first  and  then  become  purplish  black; 
and  by  the  absence  of  any  offensive  odor. 

The  watery  disintegration  associated  with  watery  soft  rot 
is  often  so  complete  that  water  runs  freely  from  crates, 
hampers,  and  even  cars  containing  affected  stock.  Due  to 
this  loss  of  water,  affected  stock  may  shrink  to  but  a  small 
portion  of  its  original  volume. 

Affected  tissue  may  seem  only  slightly  discolored  and 
rotted,  but  upon  application  of  pressure  it  is  noted  that  the 
tissue  is  completely  softened  and  that  water  escapes  with 
the  greatest  ease.  The  slimy  feeling  noted  in  connection 
with  the  slimy  soft  rot  of  succulent  tissues  is  entirely  absent. 

The  affected  plants,  the  containers,  and  even  the  car  may 
be  overrun  by  a  heavy  growth  of  loose,  cottony  or  matted 
mycelium,  which  under  proper  conditions  forms  the  sclerotia 
previously  mentioned.  The  fungus  often  is  responsible  for 
the  so-called  "nesting"  of  beans. 

Affected  celery  tissue  often  has  a  pinkish  or  rose  color, 
especially  in  the  early  stages,  and  consequently  the  rot  is 
sometimes  known  as  "pink  rot"  of  celery.  At  times  purplish 
tints  are  noticeable.  Generally,  however,  the  diseased  tissue 
is  yellowish  or  brown. 

In  typical  field  attacks  upon  lettuce,  which  are  known  as 
lettuce  "drop,"  or  upon  cabbage,  the  disease  begins  on  the 
stalk  near  the  ground,  or  on  the  leaves  touching  the  ground, 
progressing  from  these  to  the  stalk,  which  becomes  softened 
and  at  times  entirely  destroyed.  The  result  in  either  case  is 
a  collapse  of  the  entire  plant.  In  the  field  the  disease  is 
known  as  "foot  rot"  of  celery  because  of  the  frequent  initial 
attacks  at  the  base  of  the  plant.  However,  under  storage 
and  transit  conditions,  plants  may  be  attacked  at  any  point. 
Well  headed  cabbage  or  lettuce  often  remains  intact  be- 
cause of  the  overlapping  leaves.  Often  one  finds,  however, 
when  an  attempt  is  made  to  lift  an  affected  head,  that  it 


22  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

falls  to  pieces  quite  unlike  plants  affected  with  slimy  soft 
rot  which  tend  to  slip  out  of  one's  hand. 

On  root  crops  the  rot  is  not  as  watery  as  on  leafy  tissues. 
Under  dry  conditions,  evaporation  keeps  pace  with  the 
liberation  of  water  by  the  fungus  and  the  affected  tissue 
dries  out  and  shrinks.  Thus  the  watery  nature  of  this  rot  in 
roots  is  not  as  evident  as  in  the  case  of  leafy  or  succulent 
tissues.  However,  under  moist  conditions,  affected  root 
crops  exude  water  freely.  The  white  cottony  or  matted 
mycelium  and  the  black  sclerotia  serve  to  identify  the  dis- 
ease on  root  crops  when  the  watery  characteristics  are 
absent. 

This  rot  can  be  differentiated  from  slimy  soft  rot  by  the 
fact  that  the  latter  is  a  slimy,  slippery  decay  usually  accom- 
panied by  a  bad  odor  and  lacks  the  white  mycelium  and 
large  sclerotia  of  watery  soft  rot.  The  latter  can  be  differ- 
entiated from  gray  mold  rot  by  the  typical  powdery  gray 
moldy  outgrowth  of  the  latter.  Gray  mold  rot  is  generally 
found  on  overmature  tissues,  and  is  not  as  watery  as  the 
typical  watery  soft  rot  caused  by  Sclerotinia.  Watery  soft 
rot  progresses  at  lower  temperatures  than  does  the  soft  rot 
induced  by  Rhizopus.  Rhizopus  rot  is  prevalent  in  the  sum- 
mer and  in  overheated  cars  in  the  winter,  while  watery  soft 
rot  develops  in  refrigerated  cars. 

The  disease  is  favored  by  high  humidity  and  moderate 
temperatures.  The  original  infection  proceeds  from  the  soil. 
Lettuce  grown  under  glass,  or  plants  grown  in  crowded 
quarters,  are  especially  subject  to  infection.  The  disease 
develops  and  spreads  very  rapidly  in  transit  and  storage,  the 
fungus  passing  from  diseased  to  healthy  tissue  by  contact. 

Crop  rotation  and  soil  sanitation  and  aeration  are  control 
measures  which  can  be  applied  in  the  field.  Losses  in  tran- 
sit and  storage  may  be  reduced  by  sorting  out  and  discard- 
ing diseased  plants  and  by  thorough  ventilation.  After  the 
diseased  portions  of  affected  plants  are  trimmed  off,  the  re- 
mainder is  edible.  It  is  not  advisable  to  store  trimmed 
plants. 

Ref.:   Lettuce  (5);  (65);  (66). 

SUN-SCALD. 

OF    CUCUMBER,    HONEY    DEW    MELON,    ONION,    PEPPER,    POTATO,    TOMATO, 

AND  WATERMELON. 

Cause :    Exposure  to  the  hot  sun. 

Sun-scald  is  evidenced  by  the  death  and  discoloration  of 
a  rather  extensive  area  on  the  exposed  surface  of  the  vege- 
table. In  most  cases,  the  lesion  is  irregular  in  outline  and 
at  first  resembles  a  water-soaked  blister,  but  soon  becomes 
slightly  but  sharply  sunken  and  distinctly  bleached  in  color. 
This  bleaching  is  particularly  noticeable  in  peppers,  toma- 
toes, and  cucumbers. 

Sun-scald  is  particularly  important  from  the  market 
standpoint  because  the  scalded  areas  are  very  subject  to  the 


MARKET  DISEASES  OF  VEGETABLES.  23 

attacks  of  rot-producing  bacteria  and  fungi.  On  onions, 
scald  may  be  followed  by  slimy  soft  rot,  and  large  losses 
were  thus  incurred  in  certain  shipments  from  Stockton,  Cal., 
in  1918.  Tomato  scald  opens  the  way  for  fungous  rots  and 
was  an  important  factor  in  the  losses  in  Texas  and  Tennessee 
shipments  in  1918.  Sun-scalded  muskmelons  or  water- 
melons are  frequently  invaded  by  saprophytic  fungi  such  as 
black  mold  (Sterigmatocystis)  and  Cladosporium  or  Alter- 
naria.  Generally  these  are  surface  growths  more  or  less 
confined  to  the  dead  tissue. 

Potato  scald  is  discussed  elsewhere,  as  is  also  sun-scald 
of  bean. 

Because  of  its  predisposition  to  rot  during  transit,  scalded 
stock  could  profitably  be  culled  out  before  shipment. 

NEMATODE    DISEASE. 

OF  BEET,  CARROT,  CELERY,  PARSNIP,  POTATO,  SWEET  POTATO,  RADISH, 
RUTABAGA,  AND  TURNIP 

Cause:   A  nematode  or  eelworm  (Heterodera  radicicola). 

This  disease  affects  the  underground  parts  of  plants.  It 
may  be  recognized  on  tubers  by  small,  pimple-like  swellings 
or  by  larger  protuberances  of  the  surface,  which  ordinarily 
becomes  roughened  at  the  infected  places.  These  swellings 
when  some  distance  apart  are  circular,  but  if  occurring  close 
together  they  take  on  various  shapes  and  sizes.  On  roots 
the  disease  appears  as  definite  galls  or  knots  and  conse- 
quently is  commonly  called  root-knot. 

Eelworm-infected  tubers  and  roots  sometimes  are  con- 
fused with  those  affected  by  other  diseases  (crown-gall  of 
beets,  club-root  of  crucifers,  and  "pimply  potatoes"  due  to 
flea-beetle  injury),  which  also  cause  a  swelling  of  the  dis- 
eased tissues.  The  nematode  disease,  however,  may  usually 
be  readily  distinguished  from  other  maladies  by  the  pres- 
ence of  small,  white;  pear-shaped  nematodes,  the  adult 
females,  which  may  barely  be  seen  with  the  unaided  eye 
when  well-infested  tissues  are  broken  or  teased  apart. 

This  disease  occurs  widely  in  most  of  the  older  trucking 
sections  of  the  southern  portions  of  the  United  States  and 
in  greenhouses  everywhere. 

Plants  become  infected  in  the  field.  The  disease  does  not 
develop  or  spread  in  transit  or  storage.  Diseased  stock, 
however,  is  very  subject  to  invasion  by  secondary  organisms, 
particularly  bacteria. 

Affected  stock  may  largely  be  eliminated  by  grading.  It 
never  should  be  shipped,  not  only  because  it  is  unsightly  in 
appearance,  of  inferior  quality,  and  impaired  in  market 
value,  but  also  because  it  may  carry  the  disease  into  unin- 
fested  regions. 

Ref.  (la). 

ARTICHOKE:  GRAY  MOLD  ROT;  BOTRYTIS  ROT. 

(See  Gray  Mold  Rot). 


24  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

ASPARAGUS:    SLIMY    SOFT    ROT;    BACTERIAL   ROT. 

(See  Slimy  Soft  Rot). 

ASPARAGUS:    WATERY    SOFT   ROT;    SCLEROTINIA   ROT. 

(See  Watery  Soft  Rot) . 

BEAN:     ANTHRACNOSE. 

Cause:    A  fungus  (Colletotrichum  lindemuthianum). 

Anthracnose  is  marked  in  the  very  early  stages  by  minute 
oval  or  circular  spots  which  are  maroon  to  reddish  in  color. 
These  spots  are  not  water-soaked  as  in  the  bacterial  blight. 
They  form  ulcer-like  lesions,  which  increase  rapidly  in  size 
and,  though  circular,  often  coalesce  to  form  large  irregular 
spots.  Very  soon,  often  in  24  hours,  the  spot  becomes  darker 
in  color,  the  central  tissue  dries  up  and  shrinks,  and  a  de- 
pressed, considerably  sunken  spot  results,  with  a  black 
center  and  generally  a  reddish  border.  Under  moist  con- 
ditions the  dark  center  of  the  spot  becomes  covered  with 
orange-pink  dots  or  spore  heaps  which  may  run  together 
and  form  a  slimy  layer.  These  spore  heaps  are  borne  on 
cushions  known  as  acervuli  (singular,  acervulus).  The  bor- 
der of  the  lesion  is  sharply  marked,  especially  on  the  wax 
pod  varieties. 

From  pod  lesions  the  fungus  often  enters  the  seeds.  In 
case  of  light  attack  the  seed  shows  only  a  yellowish  spot. 
In  severe  cases  the  spots  are  yellowish,  brownish,  or  black, 
and  circular  or  irregular  in  shape,  and  are  surrounded  by  a 
reddish  zone.  They  may  be  sunken,  but  rarely  show  the 
pinkish  slime  noted  on  the  pod  spots.  The  spots  on  the  seed 
are  darker  colored  and  more  definitely  marked  than  those 
of  bacterial  blight. 

Anthracnose  occurs  in  all  varieties  of  wax  pod,  green  pod, 
pole,  navy,  kidney,  lima,  and  some  scarlet  runner  beans.  Its 
development  is  favored  by  moderately  cool  weather,  and  its 
spread,  by  wet  weather.  Since  it  is  carried  in  the  seed,  the 
disease  may  occur  in  any  bean-growing  section,  but  the 
regions  subject  to  cool,  wet  weather  are  most  seriously  af- 
fected. It  is  least  prevalent  in  the  Rocky  Mountain  and 
Pacific  Coast  States. 

The  original  infection  takes  place  in  the  field  where  both 
the  vines  and  pods  are  affected.  The  disease  develops  on 
the  pods  in  transit,  and  may  spread  under  very  moist  con- 
ditions. 

Crop  rotation  and  the  use  of  disease-free  seed  or  disease- 
escaping  varieties  are  the  only  known  effective  control 
measures.  Seed  grown  in  hot,  dry  regions  is  comparatively 
free  from  anthracnose. 

Ref.  (76);  (14);  (47). 

BEAN:     BACTERIAL   BLIGHT. 

Cause:    Bacteria  (Pseudomonas  phaseoli). 

In  the  early  stages  bacterial  blight  is  marked  by  small, 


MARKET  DISEASES  OP  VEGETABLES.  25 

water-soaked  spots  on  the  pods.  These  gradually  enlarge 
and  become  irregular  in  shape,  the  green  color  fading  as 
the  affected  tissue  dries  out.  The  lesions  may  have  an  ele- 
vated margin.  Very  soon  th,e  spots  become  reddish  brown, 
first  at  the  margins  and  then  in  the  centers.  Finally  they 
turn  a  darker  brown.  In  this  stage  the  spot  dries  out  and 
becomes  sunken.  Under  moist  conditions,  a  slime  oozes  out 
from  the  surface  of  the  water-soaked  spots.  When  dry, 
this  exudate  forms  a  translucent  or  yellow  crust.  The  bor- 
der between  healthy  and  diseased  tissue  is  not  as  sharply 
marked  as  in  bean  anthracnose,  and  is  more  irregular.  The 
presence  of  the  exudate  and  the  irregular  shape  of  the  lesion 
usually  serve  to  identify  blight. 

The  bacteria  from  the  pod  lesions  may  penetrate  and 
infect  the  seeds.  Such  seeds  are  marked  by  yellow  spots  or 
blotches  of  irregular  shape  or  by  surface  crusts  of  a  yel- 
lowish color.  These  spots  may  show  dark  red  borders  and 
at  times  a  brown  or  black  color.  Seeds  often  are  completely 
yellowed  and  shriveled. 

Bacterial  blight  occurs  in  all  bean  districts  east  of  the 
Rocky  Mountains.  Its  spread  is  favored  by  moist  warm 
weather,  though  it  can  develop  in  dry  weather.  It  causes 
severe  blighting  of  the  foliage,  and  may  kill  plants  outright. 
Pod  infection  takes  place  in  the  field,  but  the  spots  may 
develop  or  enlarge  in  transit,  and  may  predispose  the  stock 
to  slimy  soft  rot  or  watery  soft  rot. 

Blight  is  a  seed-borne  infection,  and  may  be  controlled 
only  by  the  use  of  disease-free  seed  and. the  practice  of  crop 
rotation. 

Ref.  (15);  (75). 

BEAN:     SOIL    ROT. 

Cause:    A  fungus  (Rhizoctonia). 

Soil  rot  is  characterized  by  large  lesions  generally  near 
the  end  of  the  pod  or  at  points  where  the  pod  has  been  in 
contact  with  the  ground.  The  lesions  are  large  and  irregu- 
lar in  shape  and  light  brown  in  color  with  soft,  badly-rotted 
underlying  tissues.  At  times  the  spots  are  concentrically 
marked.  Anthracnose  lesions  are  smaller  and  more  regular 
in  shape. 

Soil  rot  occurs  only  in  very  moist  seasons.  The  original 
infection  takes  place  in  the  field.  The  fungus  spreads  from 
diseased  to  healthy  pods  in  transit  under  moist  conditions 
and  often  causes  severe  "nesting."  The  coarse,  brown 
hyphae  of  the  fungus  and  the  sclerotia,  if  present,  distin- 
guish soil  rot  from  the  watery  soft  rot  induced  by  Sclero- 
tinia  and  from  the  rot  caused  by  Rhizopus,  both  of  which 
also  cause  "nesting." 

Soil  rot  is  controllable  by  careful  sorting  of  the  stock  and 
by  maintaining  a  low  temperature  and  humidity  during 
transit. 


26  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

BEAN:     RUSSET. 

Cause :    Unknown.    Non-parasitic. 

Russet  is  a  rather  prevalent  chestnut-brown  surface  dis- 
coloration of  green-pod  and  occasionally  wax-pod  beans. 
The  discolored  areas  are  of  various  shapes  and  sizes,  some- 
times involving  nearly  all  of  the  pod.  The  affected  tissue 
is  firm  and  sound,  and  is  not  at  all  sunken.  The  discolora- 
tion is  due  to  the  death  of  the  three  or  four  outer  layers  of 
cells. 

This  disease  seems  to  appear  in  beans  that  have  been  in 
transit  or  storage  for  some  time,  and  is  probably  not  of  field 
origin.  Russet  is  common  in  Florida  beans  in  the  northern 
markets.  It  is  objectionable  because  of  the  injury  to  the 
appearance  of  affected  stock. 

No  control  is  known. 

BEAN:     SUN-SCALD. 

Cause :    Exposure  to  the  hot  sun. 

This  injury  first  shows  up  on  the  exposed  side  of  the  pod 
as  minute  brown  or  reddish  parallel  streaks,  which  enlarge 
and  merge  to  form  brown  or  reddish  areas  of  varying  size. 
Sun-scald  is  not  easily  distinguished  from  bacterial  spot,  but 
is  more  likely  to  be  limited  to  one  side  of  the  pod,  and  lacks 
the  greasy  exudate  which  often  is  present  on  blight  lesions. 

Sun-scald  is  due  to  exposure  to  the  sun,  and  does  not 
occur  where  the  pods  are  shaded. 

Ref.  (41). 

LIMA   BEAN:     POD    BLIGHT. 

Cause:    A  fungus  (Diaporthe  phaseolorum). 

In  the  early  stages,  this  disease  is  characterized  by  cir- 
cular to  semi-circular  spots  of  darkened  tissue.  Later  the 
affected  tissue  becomes  studded  with  minute,  gray  eleva- 
tions. These  elevations  soon  break  the  skin  of  the  pod,  and 
emerge  as  black  pustules,  the  fruiting  bodies,  or  pycnidia, 
of  the  fungus.  The  pycnidia  may  be  arranged  concentri- 
cally or  in  chain-like  fashion.  In  advanced  stages,  the  entire 
pod  may  become  diseased  and  covered  with  pycnidia. 

Pod  blight  has  been  reported  only  in  the  Northern  Atlan- 
tic States,  and  is  not  common.  Infection  takes  place  in  the 
field,  and  the  disease  may  develop  and  progress  in  transit. 

Pod  blight  can  be  controlled  by  seed  selection  and  disin- 
fection and  by  spraying  in  the  field.  It  is  advisable  to  sort 
out  and  not  market  diseased  pods. 

Ref.  (25). 

BEAN:    RHIZOPUS    ROT. 

(See  Rhizopus  Rot). 

BEAN:    SLIMY    SOFT    ROT;    BACTERIAL    ROT. 

(See  Slimy  Soft  Rot) . 


MARKET  DISEASES  OF  VEGETABLES.  27 

BEAN:    WATERY   SOFT   ROT;    SCLEROTINIA   ROT. 

(See  Watery  Soft  Rot) . 

BEET:     BLACK   ROT. 

Cause:    A  fungus  (Phoma  betae). 

In  this  rot,  the  affected  tissue  is  coal  black,  rather  firm 
and  extends  deeply  into  the  root.  There  is  no  bad  odor. 
The  surface  becomes  somewhat  shrunken,  and  often  bears 
the  black  pycnidia  of  the  causal  fungus. 

This  disease  causes  a  leaf  spot  and  a  blight  of  the  plants 
in  the  field.  The  fungus  is  carried  with  the  seed. 

Control  consists  of  seed  and  seed-bed  sanitation  and  re- 
moval of  diseased  leaves  from  roots  previous  to  storage. 

Ref.  (17). 

BEET:     LEAF    SPOT. 

Cause:    A  fungus  (Cercospora  beticola). 

This  disease  occurs  only  on  the  leaves  where  its  lesions 
appear  as  distinctly  circular  spots  with  purple  borders  and 
tan  to  ashen  gray  centers.  Leaves  may  be  killed  by  the 
coalescence  of  numerous  lesions.  The  death  of  the  older 
leaves  may  cause  the  crown  to  elongate,  thus  affecting  the 
shape  of  the  root. 

Beet  leaf  spot  is  widespread  in  its  occurrence  and  is  of 
considerable  economic  importance  in  the  field.  In  the  sugar 
beet  crop,  it  lowers  the  efficiency  of  the  leaves  as  sugar  pro- 
ducers. In  the  market,  leaf  spot  predisposes  the  leaves  to 
the  attack  of  slimy  soft  rot. 

Spraying  with  Bordeaux  mixture  will  control  the  disease. 

Ref.  (40). 

BEET:    SLIMY    SOFT    ROT;    BACTERIAL    ROT. 

(See  Slimy  Soft  Rot). 

BEET:  GRAY  MOLD  ROT;  BOTRYTIS  ROT. 

(Se&Gray  Mold  Rot). 

BEET:    WATERY    SOFT    ROT;    SCLEROTINIA    ROT. 

(See  Watery  Soft  Rot). 

BEET:    NEMATODE    DISEASE. 

(See  Nematode  Disease). 

BEET:     MISCELLANEOUS    DISEASES. 
ROOT    ROT. 

Cause:    A  fungus  (Rhizoctonia). 

This  rot  starts  typically  from  the  crown,  and  progresses 
downward  from  the  leaf  bases. 
Ref.  417). 

SCAB. 

Cause:    A  fungus  (Actinomyces  scabies). 


28  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

Beet  scab  closely  resembles  potato  scab.  Large  corky 
brown  excrescences  are  produced.  Sugar  beets  and  mangels 
are  susceptible. 

This  disease  is  uncommon  in  the  market. 

BRUSSELS    SPROUTS:    BLACK    LEAF    SPOT. 

(See  Cabbage  Black  Leaf  Spot) . 

BRUSSELS    SPROUTS:    RING-SPOT. 

(See  Cauliflower  Ring-Spot). 

CABBAGE:     BLACK    LEAF    SPOT. 

Cause:    A  fungus  (Alternaria  brassicae). 

In  the  early  stages,  this  disease  is  characterized  by 
minute,  circular,  shiny,  brown  to  black  spots.  Later  these 
spots  enlarge  and  lose  their  circular  shape.  The  lesions 
generally  are  somewhat  concentrically  marked  in  target 
fashion  and,  under  moist  conditions,  may  be  covered  by  a 
growth  of  brown  to  black  mold.  Generally,  if  affected  heads 
are  kept  in  a  dry  place,  the  centers  of  the  spots  fall  out  and 
leave  holes. 

The  lesions  are  more  pronounced  and  more  common  on 
the  outer  leaves,  but  under  moist  conditions,  the  fungus  may 
penetrate  from  leaf  to  leaf  and  often  may  afford  points  of 
attack  for  the  bacteria  of  slimy  soft  rot. 

Infection  occurs  in  the  field,  and  the  disease  develops  in 
transit  and  storage. 

Disinfection  of  storage  houses,  care  in  handling,  and  a 
regulation  of  temperature  and  moisture  conditions  will  con- 
trol the  disease  in  storage.  The  spots  do  not  render  cabbage 
unfit  for  transit  and  storage  if  the  affected  leaves  are 
trimmed  off. 

Ref.  (26). 

CABBAGE:     BLACK    ROT. 

Cause:    Bacteria  (Pseudomonas  campestris). 

Black  rot  is  characterized  by  a  black  discoloration  of  the 
water-conducting  tissue  of  the  plant.  Sometimes  the  dis- 
coloration occurs  only  as  a  ring  in  the  stalk,  but  not  infre- 
quently it  extends  into  the  leaf  midrib  and  veins.  This 
discoloration  in  the  stalk  can  be  seen  easily  if  a  fresh  section 
is  cut,  and  its  progress  into  the  leaves  can  be  noted  by  break- 
ing the  leaves  from  the  stem,  which  will  reveal  a  group  of 
black  dots  in  the  leaf  scars.  Badly  affected  leaves  have  a 
steel  gray  or  purplish  hue,  due  to  partial  masking  of  the 
blackened  veins  by  the  white  or  yellowish  leaf  tissue. 

If  no  secondary  rots  set  in,  the  disease  may  show  itself 
as  a  slowly  progressing  rot  which  does  not  necessarily  pro- 
ceed from  the  outside  leaves  as  in  slimy  or  watery  soft  rot, 
but  may  appear  in  the  covered  leaves,  even  in  the  heart  of 
the  head.  Generally,  however,  a  typical  slimy  soft  rot  sets 


MARKET  DISEASES  OF  VEGETABLES.  29 

in,  proceeding  either  from  the  outside  or  inside,  and  the 
head  rots  rapidly  with  a  very  offensive  odor.. 

This  disease  occurs  in  all  cabbage-growing  regions.  Infec- 
tion takes  place  in  the  field.  The  bacteria  enter  the  plant 
at  the  margins  of  the  leaves,  proceed  downward  through 
the  veins  to  the  main  stalk,  and  then  upward  into  the  head. 

The  disease  develops  in  transit  and  storage.  Affected 
stock  is  very  subject  to  secondary  rots,  and  as  a  result  is  a 
menace  to  healthy  stock. 

Control  of  the  disease  in  the  field  consists  of  seed  disin- 
fection, seedbed  sanitation,  and  crop  rotation.  Severely 
affected  stock  is  unfit  for  food.  It  is  not  advisable  to  store 
or  ship  slightly  affected  stock. 

Ref.  (61);  (26). 

CABBAGE:     FREEZING    INJURY. 

Cause :    Exposure  to  low  temperatures. 

Freezing  injury  is  marked  by  a  glassy  yellowish  appear- 
ance of  the  affected  tissues. 

Affected  stock,  if  thawed  rapidly  in  a  warm  place,  or  if 
kept  in  a  moist  atmosphere,  is  soon  destroyed  by  slimy  soft 
rot.  Therefore  it  is  not  suitable  for  storage.  It  is  generally 
assumed  that  cabbage  can  be  frozen  once  or  twice,  if  thawed 
out  properly,  without  any  injury  except  a  slight  shrinkage 
and  flabbiness.  The  outer  leaves  can  be  frozen  and  thawed 
without  injury,  but  if  the  freezing  extends  to  the  interior 
tender  tissues,  these  are  killed  and,  upon  thawing,  fall  a 
ready  prey  to  slimy  soft  rot. 

Generally  all  frozen  heads  which  do  not  show  a  glassy, 
yellowish  ring  in  the  tissue  of  the  stalks  upon  thawing  are 
fit  for  marketing  for  immediate  consumption.  This  is  not 
a  positive  test,  however,  since  not  all  affected  heads  show 
a  discoloration  or  decay  of  the  stalk. 

CABBAGE:     LEAF    SPECK. 

Cause :    Not  known ;  probably  non-parasitic. 

Leaf  speck  consists  of  small,  sharply-sunken,  shiny,  brown 
spots  or  black  specks  which  may  occur  on  all  leaves  of  an 
affected  head.  Speck  can  be  differentiated  from  black  leaf 
spot  by  the  smaller  size  of  the  spots,  and  by  the  absence  of 
concentric  rings,  or  any  black  fungous  outgrowth. 

Leaf  speck  occurs  in  cabbage  from  all  sections,  and  is  very 
severe  in  some  Florida  stock. 

Nothing  is  known  about  the  cause,  point  of  origin,  and 
conditions  favoring  the  development  of  the  disease. 

No  control  measures  are  known.  It  is  advisable  to  sort 
cabbage  carefully  because  affected  heads  have  a  lower 
market  value. 

CABBAGE:    SUN-SCALD. 

(See  Sun-Scald). 


30  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

CABBAGE:    GRAY    MOLD    ROT;    BOTRYTIS    ROT. 

(See  Gray  Mold  Rot) . 

CABBAGE:    RHIZOPUS    ROT. 

(See  Rhizopus  Rot). 

CABBAGE:    SLIMY    SOFT    ROT;    SOFT    ROT;    BACTERIAL   ROT. 

(See  Slimy  Soft  Rot) . 

CABBAGE;  WATERY  SOFT  ROT;  SCLEROTINIA  ROT. 

(See  Watery  Soft  Rot). 

CARROT:  GRAY  MOLD  ROT;  BOTRYTIS  ROT. 

(See  Gray  Mold  Rot  and  Artichoke  Gray  Mold  Rot) . 

CARROT:    RHIZOPUS    ROT. 

(See  Rhizopus  Rot) . 

CARROT:    SLIMY    SOFT    ROT;    SOFT    ROT. 

(See  Slimy  Soft  Rot) . 

CARROT:  WATERY  SOFT  ROT;  SCLEROTINIA  ROT. 

(See  Watery  Soft  Rot). 

CARROT:    NEMATODE    DISEASE. 

(See  Nematode  Disease). 

CAULIFLOWER   AND   BRUSSELS    SPROUTS:    RING-SPOT. 

Cause:    A  fungus  (Mycosphaerella  brassicicola). 

The  symptoms  of  this  disease  of  cauliflower  are  small 
definitely  circular  spots  on  the  leaves.  They  are  visible  on 
both  sides  of  the  leaf,  have  light  brown  or  grayish,  dry 
centers,  and  are  surrounded  by  olive-green  or  blue-green 
borders  which  shade  off  into  the  natural  color  of  the  leaf. 
When  the  leaves  turn  yellow,  the  spots  retain  their  green 
borders  and  become  very  conspicuous  against  the  yellow 
background.  The  borders  of  the  lesions  are  frequently 
raised,  and  may  show  concentric  circles.  Very  minute, 
black  dots,  pycnidia,  cover  the  outer  edges  of  the  spots  on 
both  surfaces  of  the  leaves.  They  are  densely  crowded  in 
the  outer  parts  of  the  lesions,  but  are  more  scattered  or 
absent  in  the  centers  of  the  spots. 

Ring-spot  is  a  field  disease  on  the  Pacific  Coast.  Infec- 
tion takes  place  in  the  field,  but  the  lesions  may  develop 
and  enlarge  during  transit. 

This  disease  causes  premature  yellowing  and  death  of 
the  leaves  and  thus  affects  the  quality  of  the  stock. 

Ref.  (52). 


MARKET  DISEASES  OF  VEGETABLES.  31 

CELERY:     BACTERIAL    LEAF    SPOT. 

Cause:     Bacteria. 

This  disease  is  characterized  by  shiny,  dark-brown  irregu- 
lar, translucent  or  parchment-like  spots  on  the  leaves. 
Often  these  lesions  extend  along  the  veins  and  down  the 
petioles  causing  a  water-soaked  condition.  This  disease 
causes  a  premature  yellowing  and  death  of  the  leaves.  The 
lesions  of  this  disease  can  be  differentiated  from  the  early 
blight  lesions  by  the  ashen  gray,  opaque  centers  of  the 
latter  and  from  late  blight  lesions  by  the  absence  of  the 
black  shiny  dots  or  pycnidia. 

Bacterial  leaf  spot  occurs  in  Michigan  and  New  York 
celery. 

Infection  takes  place  in  the  field  and  the  disease  may 
develop,  but  does  not  spread  in  transit  or  storage. 

Severely  affected  stock  is  discriminated  against  because 
of  its  unsightliness  and  because  the  petiole  lesions  destroy 
the  edible  parts  of  the  plant. 

Spraying  with  Bordeaux  will  control  the  disease. 

CELERY:     EARLY    BLIGHT. 

Cause:    A  fungus  (Cercospora  apii). 

Early  blight  is  characterized  by  irregular,  slate-colored 
spots  on  the  leaves,  with  ashen-gray  to  tan  centers.  These 
can  be  distinguished  from  late  blight  lesions  by  their  larger 
size  and  the  absence  of  the  conspicuous  black  dots  or 
pycnidia.  Generally  early  blight  occurs  only  on  the  leaves, 
while  late  blight  occurs  very  commonly  on  the  petiole  as 
well  as  on  the  leaf  blade.  At  times  early  blight  occurs  on 
the  petioles  as  elongated,  tan,  sunken  areas,  and  causes  a 
wilting  and  drying  out  of  the  leaf  and  petiole.  This  disease 
occurs  in  all  celery  districts,  but  is  most  common  in  Florida 
celery.  It  is  favored  by  hot,  dry  weather. 

Early  blight  starts  as  a  field  infection,  and  develops  in 
transit  or  storage.  Unlike  late  blight,  it  does  not  lead  to  a 
rot,  but  causes  the  tissues  to  dry  out  and  shrivel. 

Severely  affected  stock  is  unsightly  and  its  market  value 
is  reduced. 

Early  blight  can  be  controlled  by  spraying  with  Bordeaux 
mixture. 

CELERY:  GRAY  MOLD  ROT;  BOTRYTIS  ROT. 

(See  Gray  Mold  Rot). 

CELERY:     LATE    BLIGHT. 

Cause:    A  fungus  (Septoria  petroselini) . 

Late  blight  is  characterized  by  small,  irregular,  brown 
spots  on  the  leaf  blade  and  petiole.  Under  transit  condi- 
tions, the  lesions  may  be  dark  green  and  water-soaked. 
The  centers  of  the  spots  bear  small,  black,  glistening  dots, 
the  fruiting  bodies  or  pycnidia  of  the  fungus.  This  disease 


32  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

can  be  differentiated  from  early  blight  and  bacterial  leaf 
spot  by  the  presence  of  the  shiny  pycnidia  and  the  more 
common  occurrence  of  spots  on  the  petioles,  where  the 
pycnidia  are  even  more  conspicuous  than  on  the  leaf  lesions. 

This  disease  occurs  generally  in  all  celery  districts,  espe- 
cially in  California,  Florida,  Michigan,  and  New  York.  It 
is  favored  by  cool,  moist  weather. 

The  fungus  overwinters  on  the  seed  and  in  the  soil.  Late 
blight  spreads  in  the  field  during  the  growing  season,  and 
although  the  original  infection  takes  place  in  the  field,  the 
disease  develops  and  spreads  in  transit  and  storage,  leading 
to  a  soft  rot  of  the  leaf  blades  and  petioles. 

Severely  affected  stock  is  unfit  for  market  and  storage 
purposes. 

Crop  rotation,  use  of  disease-free  seed,  and  proper  spray- 
ing will  control  the  disease.  It  is  advisable  to  discard 
severely  diseased  plants  because  of  the  continued  develop- 
ment of  the  disease  at  low  temperatures. 

Ref.  (11);  (55). 

CELERY:  SLIMY  SOFT  ROT;  BACTERIAL  ROT. 

(See  Slimy  Soft  Rot) . 

CELERY:   WATERY  SOFT  ROT;   SCLEROTINIA  ROT;   FOOT  ROT; 
PINK    ROT;    RIB    ROT. 

(See  Watery  Soft  Rot) . 

CELERY:    BLACK    HEART. 

Cause :    Unbalanced  water  relations. 

In  the  earliest  stages  this  .disease  is  marked  by  shiny, 
light  brown  lesions  on  the  blades  of  the  youngest  leaves. 
Very  often  these  are  not  apparent  until  the  heart  of  the 
plant  is  dissected,  since  the  innermost,  most  completely  pro- 
tected leaves  frequently  are  the  only  ones  affected.  Later 
the  lesions  enlarge  so  as  to  involve  the  entire  leaf  blade,  and 
become  very  moist  and  turn  black,  the  whole  heart,  even 
the  entire  stalk,  becoming  involved  if  sufficient  time  is 
allowed.  The  advanced  symptoms  of  the  disease  are  caused 
by  bacteria  of  the  Bacillus  caratovorus  type,  which  invade 
the  tissue  killed  by  the  unbalanced  water  relations  of  the 
plant. 

Black  heart  originates  in  the  field.  Its  evil  consequences 
are  so  well  realized  by  shippers  that  most  affected  stock  is 
culled  out  before  shipping.  Whether  or  not  stock  will  de- 
velop black  heart  depends  upon  the  plant  itself,  upon  the 
nature  of  the  soil  on  which  the  crop  is  grown,  and  upon  the 
weather.  In  Florida  the  disease  is  most  severe  in  late  season 
plants  of  the  Golden  Heart  variety. 

Ref.  (60). 

CELERY:    NEMATODE    DISEASE. 

(See  Nematode  Disease). 


MARKET  DISEASES  OF  VEGETABLES.  33 

CUCUMBER    AND    MUSKMELON;    ANTHRACNOSE. 

Cause:    A  fungus  (Colletotrichum  lagenarium). 

On  cucumbers  the  anthracnose  lesions  are  found  in  the 
market  as  circular,  sunken,  water-soaked  spots  which 
usually  bear  a  slimy,  orange-pink  coating  of  spore  masses. 
As  the  rotted  tissue  dries  out,  the  surface  may  crack. 

On  Honeydew  muskmelons  the  oval,  light  gray  lesions 
with  concentric  rings  of  pink  or  black  dots  (acervuli)  are 
very  conspicuous.  Large  lesions  become  sunken,  and  the 
central  tissue  often  cracks  open,  affording  a  port  of  entry 
for  other  fungi. 

On  netted  cantaloupes,  the  lesions  are  sharply  sunken  but 
not  very  conspicuous  until  the  salmon-colored  spore  masses 
appear. 

The  same  fungus  causes  anthracnose  of  watermelon  (dis- 
cussed elsewhere). 

Anthracnose  is  a  field  disease  occurring  on  leaves,  stems, 
and  fruits.  Infection  proceeds  from  infested  seed  or  soil, 
and  the  disease  spreads  during  wet  weather.  Fruit  infec- 
tion takes  place  in  the  field  and  the  lesions  enlarge  in  transit, 
causing  serious  blemishing.  Frequently,  secondary  rots 
enter  through  the  anthracnose  spots. 

Anthracnose  is  of  widespread  occurrence.  In  the  market 
it  has  been  noted  commonly  on  Louisiana  cucumbers  and 
Colorado  Honeydew  and  Osage  muskmelons. 

Affected  fruits  are  unsightly  and  rapidly  become  un- 
salable. 

The  disease  can  be  controlled  by  crop  rotation,  use  of 
disease-free  seed,  and  spraying  with  Bordeaux  mixture.  It 
is  advisable  not  to  ship  fruits  showing  any  signs  of  the  dis- 
ease because  of  its  rapid  development  in  transit. 

Ref.  (21). 

CUCUMBER:     BACTERIAL   SPOT. 

Cause:     Bacteria  (Bacterium  lachrymans). 

The  lesions  of  bacterial  spot  appear  as  small  greasy  or 
water-soaked  spots,  usually  showing  a  small  whitish  dot  in 
the  center.  The  diseased  spots  may  enlarge  and  lead  to  a 
secondary  soft  rot  of  rather  large  areas.  Often  a  jelly-like 
mass  of  exudate  is  formed  on  these  lesions.  Under  certain 
conditions,  such  rotted  tissue  may  dry  out,  leaving  cavities 
in  the  surface  of  the  fruit. 

Bacterial  spot  is  a  common  and  widespread  disease  of  the 
vines  causing  what  is  known  in  the  field  as  angular  leaf  spot. 
The  disease  is  carried  with  the  seed  and  spreads  in  the  field 
in  wet  weather.  Fruits  become  infected  in  the  field,  and  the 
disease  may  progress  but  does  not  spread  during  transit. 

The  disease  may  be  controlled  by  seed  disinfection,  crop 
rotation,  and  spraying  with  Bordeaux  mixture. 

Ref.  (6);  (62);  (8). 


34  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

CUCUMBER:     MOSAIC. 

Cause :    Unknown. 

Cucumbers  affected  with  mosaic  may  be  variously  mis- 
shapen, often  bearing  large  warts.  They  are  often  dis- 
tinctly mottled  in  color.  A  common  type  is  a  combination 
of  green  warts  on  a  white  or  yellowish  background. 

Mosaic  is  a  widespread  and  very  destructive  disease  of 
the  vines  which  greatly  reduces  the  yield.  It  is  extremely 
communicable  and  is  spread  by  insects. 

Usually  the  more  severely  affected  fruits  do  not  reach  the 
market.  So  far  as  known,  the  edibility  and  keeping  quali- 
ties of  affected  fruits  are  not  impaired,  but  the  market  value 
is  materially  lowered. 

No  practical  control  is  known. 

Ref.  (13);  (22);  (31). 

CUCUMBER:     SCAB. 

Cause:    A  fungus  (Cladosporium  cucumerinum). 

The  symptoms  of  this  disease  on  the  fruits  are  small,  cir- 
cular, sunken  lesions  covered  with  a  greenish  velvety 
growth  of  mold.  Drops  of  a  red  gummy  exudate  may  be 
formed  on  these  spots.  The  disease  is  not  simply  a  scab  as 
the  name  would  imply,  since  the  tissues  are  rather  deeply 
involved. 

The  fungus  attacks  the  vines,  and  fruit  infection  occurs 
in  the  field.  Young  growing  parts  are  very  subject  to 
attack.  The  disease  is  very  important  in  the  pickle  crop, 
where  it  becomes  severe  late  in  the  season.  It  is  favored 
by  cool,  moist  weather. 

Ref.  (12). 

CUCUMBER:    SUN-SCALD. 

(See  Sun-Scald). 

EGG    PLANT:     FRUIT    ROT. 

Cause:     A  fungus  (Phomopsis  vexans). 

At  first  fruit  rot  consists  of  small,  circular  or  oval  spots. 
Usually  the  lesions  are  at  first  much  lighter  in  color  (tan  or 
gray)  than  the  surrounding  tissue.  Later  the  lesions  become 
dark  brown  and  sunken,  and  under  favorable  conditions 
increase  very  rapidly  in  size.  By  the  coalescence  of  such 
lesions,  much  or  all  of  the  surface  of  a  fruit  may  be  involved. 
Small,  brown  to  black,  pimple-like  pustules  or  pycnidia 
break  through  the  surface  and  cover  the  inner  and  older 
zones  of  affected  tissue.  The  affected  regions  are  brown 
and  softened.  At  times  they  are  quite  dry,  suggesting  a 
dry  rot. 

Fruit  rot  occurs  in  all  egg  plant  growing  regions,  but  is 
especially  severe  in  the  South. 

The  disease  occurs  on  the  plants  in  the  field,  where  it 
attacks  leaves,  stems,  and  fruit,  and  is  known  as  leaf  spot, 


MARKET  DISEASES  OF  VEGETABLES.  35 

stem  blight,  and  fruit  rot.  The  original  infection  of  the  fruit 
takes  place  in  the  field,  but  the  disease  develops  and  spreads 
in  transit  and  often  causes  heavy  losses. 

It  is  not  safe  to  ship  spotted  fruits. 

Ref.  (23). 

EGG    PLANT:    RHIZOPUS    ROT. 

(See  Rhizopus  Rot). 

LETTUCE:     BLACK    ROT. 

Cause :     Bacteria. 

Black  or  brown  spots  or  irregular  patches  on  the  outer 
leaves,  increasing  in  size  under  proper  conditions  until  entire 
leaves  are  involved,  are  the  symptoms  of  this  disease.  Later 
the  inner  leaves  may  be  attacked,  and  a  soft  dark  brownish 
rot  of  the  head  may  result. 

This  is  a  field  disease  reported  from  Florida  affecting 
seedlings  and  older  plants.  It  may  develop  during  transit. 

Other  bacterial  field  diseases  of  lettuce  have  been  re- 
ported from  North  Carolina  and  Louisiana. 

The  relation  of  these  field  diseases  to  the  slimy  soft  rot 
prevalent  in  the  market  has  not  yet  been  determined. 

Ref.  (60). 

LETTUCE:  GRAY  MOLD  ROT;  BOTRYTIS  ROT. 

(See  Gray  Mold  Rot  and  Cauliflower  Gray  Mold  Rot). 

LETTUCE,    ENDIVE,    ESCAROLE,    AND    CHICORY:    SLIMY    SOFT 
ROT;    BACTERIAL   ROT. 

(See  Slimy  Soft  Rot). 

LETTUCE:     WATERY     SOFT    ROT;     SCLEROTINIA    ROT;     DROP; 

DAMP-OFF. 

(See  Watery  Soft  Rot). 

LETTUCE:     RUSSET. 

Cause :    Not  known,  probably  non-parasitic. 

This  disease  is  characterized  by  small  reddish  to  russet 
spots  or  streaks  which  may  occur  on  practically  all  of  the 
leaves  of  an  affected  head.  The  brown  streaks  usually  occur 
along  the  large  veins  of  the  leaves.  The  vascular  bundles 
in  the  stalk  and  in  the  petioles  may  also  be  discolored. 

Russet  occurs  in  lettuce  from  all  regions. 

Nothing  is  known  about  control  of  the  disease. 

It  is  advisable  to  sort  carefully  before  shipping  because 
the  presence  of  russeted  heads  reduces  the  value  of  a  ship- 
ment. 

LETTUCE:     TIP    BURN. 

Cause:     Non-parasitic  (irregular  water  supply). 

This  disease  is  characterized  by  the  dead,  brown  borders 


36  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

of  the  leaves  throughout  the  head.  It  is  found  in  head  let- 
tuce from  all  except  the  Boston  district. 

Tip  burn  is  a  field  disease  probably  caused  by  an  irregular 
water  supply.  The  injury  is  most  likely  to  occur  when 
bright  warm  weather  follows  a  period  of  cloudy  or  rainy 
weather,  and  is  much  worse  on  certain  soils  than  on  others. 
The  disease  seems  to  be  least  prevalent  on  a  soil  with  a  high 
sand  and  low  clay  content,  combined  with  a  high  water- 
holding  capacity.  In  such  a  soil,  lettuce  becomes  deep 
rooted,  and  can  apparently  obtain  water  with  sufficient 
rapidity  to  prevent  injury  from  too  rapid  transpiration.  In 
the  Imperial  Valley  of  California,  this  disease  appears  to  be 
associated  with  an  excess  of  alkali  in  the  soil. 

Tip  burn  often  predisposes  affected  stock  to  slimy  soft  rot 
during  transit  and  storage.  The  slimy  soft  rot  starts  in  the 
dead  tissues,  especially  in  the  interior  of  the  head  where 
moist  conditions  prevail.  Sometimes  the  rot  gets  a  foothold 
even  in  the  growing  plant. 

No  effective  method  of  control  has  been  established  for 
tip  burn.  A  well-regulated  water  supply  and  the  use  of 
varieties  properly  adapted  to  the  soil  and  climatic  condi- 
tions are  important  considerations. 

Ref.  (19);  (20). 

LETTUCE:     MISCELLANEOUS    DISEASES. 
DOWNY    MILDEW. 

Cause:    A  fungus  (Bremia  lactucae). 

The  symptoms  of  this  disease  are  sharply  angular  leaf 
spots,  yellowish  to  brown  when  viewed  from  above,  and 
bearing  on  the  lower  surfaces  a  white  felt-like  outgrowth  of 
mold,  the  spores  and  spore-bearing  mycelium  of  the  fungus. 

Downy  mildew  occurs  on  lettuce  grown  under  glass  and 
on  the  field  crop  where  moist  cool  weather  prevails,  as  in 
the  Colma  district  in  California.  In  head  lettuce,  the  inner 
as  well  as  outer  leaves  are  attacked.  This  disease  is  of  some 
importance  because  of  its  direct  attack  on  the  edible  leaves 
and  because  of  its  tendency  to  predispose  the  tissues  to  slimy 
soft  rot. 

LEAF    SPOT. 

Cause :    A  fungus  (Septoria  consimilis) . 

This  disease  causes  brown  spots  on  the  older  leaves  bear- 
ing black  points,  the  pycnidia  of  the  fungus.  It  occurs  on 
garden  varieties  late  in  the  season,  and  is  of  little  impor- 
tance. 

LEAF  SPOT. 

Cause:    A  fungus  (Cercospora  lactucae). 

Small  tan-colored  spots  on  the  older  leaves  are  the  symp- 
toms of  this  disease,  which  has  been  noted  in  the  San  Fran- 
cisco market. 

SHOT    HOLE    OR    ANTHRACNOSE. 

Cause:    A  fungus  (Marssonia  panattoniana). 


MARKET  DISEASES  OF  VEGETABLES.  37 

Small  brown  spots  on  the  leaves,  from  which  the  dry  cen- 
ters often  crack  and  fall  out,  are  characteristic  of  this  dis- 
ease, which  occurs  on  greenhouse  lettuce. 

Ref.  (2). 

MUSKMELON:    (HONEYDEW    AND    CASABA):    FRUIT    SPOT. 

Cause:    A  fungus  (Alternaria). 

On  Honeydew  melons,  this  disease  appears  first  as  small 
water-soaked  or  chestnut-brown  spots  on  the  surface.  As 
these  enlarge,  they  become  more  oval  in  shape  and  may 
have  wide  water-soaked  borders.  Later  the  lesions  become 
more  or  less  sunken  and  usually  develop  black  centers. 
Under  humid  conditions  a  velvety  surface  growth  of  mold  is 
produced  on  the  lesions.  This  mold  is  at  first  gray,  but  soon 
becomes  dark  greenish  gray  and  later  dark  brown  or  almost 
black. 

Continued  development  and  coalescence  of  these  lesions 
lead  to  an  extensive  shallow  rot  of  the  rind  accompanied  by 
a  cracking  of  the  surface.  The  affected  tissue  is  at  first  very 
soft  and  watery,  later  becoming  yellowish  and  very  dry, 
tough,  and  leathery.  The  rot  eventually  penetrates  through 
the  rind  into  the  edible  pulp  below. 

The  symptoms  on  the  Casaba  melon  are  essentially  similar 
to  those  on  the  Honeydew  melon.  On  the  striped  Christmas 
Casaba  melon,  the  lesions  are  brown  and  less  conspicuous 
and  the  surface  growth  of  mold  is  not  common. 

Fruit  spot  lesions  differ  from  those  of  anthracnose  in  the 
absence  of  acervuli  and  in  the  moldy  outgrowth  usually 
present. 

This  disease  was  found  very  prevalent  during  the  fall  of 
1918  on  Colorado  Honeydew  melons,  and  on  both  the  Ca- 
saba and  Christmas  Casaba  melons  from  Turlock,  Cal. 

The  source  of  infection  is  not  known.  The  lesions  appear 
during  transit  and  storage  and  become  very  conspicuous  in 
the  market,  not  only  detracting  from  the  appearance  of  the 
melons  but  also  causing  an  objectionable  surface  rot.  In 
addition,  the  lesions  also  serve  as  points  of  entry  for  other 
rot-producing  organisms. 

No  control  measures  are  known. 

MUSKMELON:    SUN-SCALD. 

(See  Sun-Scald). 

MUSKMELON    (CANTALOUPE):    MISCELLANEOUS    DISEASES. 
BACTERIAL    SOFT    ROT. 

Cause :    Bacteria. 

Wounds  and  fruit  spot  lesions  may  open  the  way  for  the 
entrance  of  bacteria  which  cause  a  soft  rot  of  the  tissues. 
This  rot  is  very  soft  and  mushy  and  the  tissue  appears  water- 
soaked.  , 

FUSARIUM    ROT. 

Cause:    A  fungus  (Fusarium). 


38  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

This  is  a  rapidly  progressing  rot  usually  characterized 
externally  by  a  dense  and  profuse  outgrowth  of  pinkish 
white  mold.  The  rotted  tissue  is  rather  dry,  and  the  pink 
mycelium  may  cause  the  entire  rotted  area  to  appear  pinkish 
in  color.  Other  types  of  Fusarium  rots  may  occur  in  the 
field.  These  rots  progress  more  rapidly  than  the  rot  caused 
by  Alternaria. 

GREEN  MOLD  ROT. 

Cause:    A  fungus  (Cladosporium). 

This  disease  occurs  very  frequently  on  cantaloupes  after 
they  have  been  in  transit  a  long  time.  It  is  characterized 
by  a  green,  velvety  fungous  growth,  which  causes  a  slowly 
progressing  rot. 

MUSKMELON     (CANTALOUPE     AND     HONEYDEW): 
ANTHRACNOSE. 

(See  Cucumber  Anthracnose). 

MUSKMELON    (HONEYDEW):    BLACK   MOLD    ROT. 

Cause:    A  fungus  (Alternaria). 

This  is  marked  by  a  brown  to  black,  velvety  surface 
growth  of  the  fungus.  The  fungus  usually  invades  tissue 
killed  by  sun-scald  and  causes  a  rot  of  the  underlying  tissues. 
This  rot  is  also  very  common  on  watermelons  affected  by 
sun-scald. 

ONION:    BLACK    MOLD    ROT. 

Cause :    A  fungus  (Sterigmatocystis  niger) . 

Black  mold  is  characterized  by  black,  powdery  masses  on 
or  between  the  scales.  When  these  masses  occur  between 
the  scales  they  have  a  tendency  to  follow  the  veins. 

Affected  stock  may  show  no  symptoms  other  than  the 
presence  of  this  black  powder.  At  times  sunken  and  dis- 
colored areas  are  found  underlying  the  powdery  black 
masses.  Under  dry  conditions  the  affected  tissue  is  papery 
and  brittle  and  sometimes  highly  colored. 

Although  commonly  called  "smut,"  this  disease  should 
not  be  confused  with  true  smut.  The  latter  is  rarely  found 
on  the  market  except  on  sets,  and  is  marked  by  black,  pow- 
dery masses  within  the  scale  tissues. 

All  varieties  of  onions  are  susceptible.  The  disease  is 
very  common  on  California  and  Texas  onions.  Infection 
occurs  in  the  field,  though  the  fungus  continues  to  grow  in 
storage. 

As  a  rot,  this  disease  under  dry  conditions  usually  is  of 
minor  importance,  but  as  a  blemish  it  causes  very  serious 
depreciation  in  value  of  the  affected  stock.  Under  moist 
conditions  the  fungus  may  cause  severe  rotting. 

Since  this  disease  does  not  progress  very  rapidly,  affected 
bulbs  can  probably  be  held  for  some  time  if  they  are  kept 


MARKET  DISEASES  OF  VEGETABLES.  39 

in  very  dry  storage  at  32°  to  35°  F.,  preferably  in  slatted 
crates  rather  than  in  bags. 
Ref.  (74). 

ONION:    GRAY    MOLD    ROT;    BOTRYTIS    ROT. 

(See  Gray  Mold  Rot). 

ONION:     NECK    ROT. 

Cause:    Fungi  (Botrytis;  Sclerotium). 

This  is  a  semi-watery  rot  followed  by  a  shrinking  and 
shriveling  of  the  scales.  The  rot  occurs  typically  as  a  neck 
rot  in  the  field,  while  in  storage  other  regions  of  the  bulb 
also  may  be  attacked.  A  gray  moldy  growth  and  hard, 
grayish  to  black  masses  of  the  fungus  (sclerotia)  develop 
on  the  outside  of  the  scales.  Neck  rot  is  an  example  of  the 
gray  mold  rot  of  vegetables  elsewhere  described. 

Neck  rot  has  a  tendency  to  rot  all  scales  uniformly  down- 
ward rather  than  to  follow  certain  scales  as  does  slimy  soft 
rot.  Typical  neck  rot  is  especially  conspicuous  in  white 
onions.  In  red  and  yellow  varieties,  the  infection  may  be 
confined  to  the  inner  scales,  and  external  neck  rot  symptoms 
may  be  lacking.  In  colored  varieties,  the  soft  rotted  condi- 
tion is  often  found,  and  the  diseased  flesh  frequently  be- 
comes pinkish,  but  the  gray  mold  growth  and  sclerotia  are 
less  commonly  found.  Unlike  slimy  soft  rot,  neck  rot  does 
not  have  a  foul  odor. 

Infection  takes  place  in  the  field,  at  or  shortly  after  the 
harvest.  The  fungus  enters  the  cut  necks  of  bulbs,  and 
gradually  progresses  downward.  The  rot  develops  in  stor- 
age under  moist  conditions.  Chilled  or  frozen  onions  and 
scallions  are  subject  to  neck  rot.  In  chilled  onions,  the  rot 
is  more  frequent  in  places  other  than  the  neck. 

If  onions  show  a  high  percentage  of  neck  rot  in  storage, 
transit,  or  market,  disposal  for  immediate  consumption  is 
advised. 

The  disease  can  be  controlled  by  prompt  curing  of  the 
crop  and  by  storage  in  a  dry  place  at  32°  to  35°  F.  It  is 
destructive  in  onion  sets  as  well  as  in  table  stock. 

Ref.  (48). 

ONION:     SLIMY    SOFT    ROT. 

Cause:    Bacteria  (Bacillus  carotovorus  group). 

This  is  a  very  soft,  mushy  rot  of  the  scales,  which  pro- 
gresses downward  from  the  neck  and  is  accompanied  by  a 
very  repulsive  odor.  Often  it  is  confined  to  only  one  or  two 
scales  in  the  interior  of  the  bulb.  Lesions  may  occur  any- 
where, however,  especially  if  the  tissues  have  been  killed 
by  sun-scald  or  bruising. 

Slimy  soft  rot  progresses  faster  than  neck  rot,  and  is  not 
accompanied  by  a  gray  mold  and  sclerotia  as  is  neck  rot. 
Neither  does  it  progress  uniformly  downward  destroying  all 


40  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

scales  as  does  neck  rot,  but  usually  follows  certain  scales 
all  the  way  around. 

Slimy  soft  rot  occurs  in  all  onion-growing  districts  in  the 
United  States,  and  is  most  common  in  onions  harvested  dur- 
ing warm,  rainy  seasons,  or  in  onions  sun-scalded  during  the 
curing  process.  It  is  also  very  common  in  Spanish  onions. 
It  is  claimed  by  growers  that  yellow  varieties  are  more  sus- 
ceptible than  red.  Careful  handling  to  avoid  sun-scald  and 
bruising  during  the  harvesting  operation  is  of  primary  im- 
portance as  a  preventive  measure. 

In  badly  affected  shipments,  immediate  drying  of  the 
stock  will  check  the  progress  of  the  rot.  This  may  be  done 
by  dumping  the  sacks  at  once  and  spreading  the  contents. 

Ref.  (67). 

ONION:     SMUDGE. 

Cause:    A  fungus  (Colletotrichum  circinans). 

Smudge  or  anthracnose  is  a  disease  of  white  onions  char- 
acterized by  black  blotches  or  aggregations  of  minute  black 
dots  on  the  outer  scales.  Each  one  of  the  minute  dots  is  an 
acervulus  (plural,  aceryuli).  These  acervuli  are  often  ar- 
ranged in  concentric  rings.  In  severe  cases,  the  smudgy 
spots  are  so  extensive  that  the  side  of  the  onion  appears 
smoked.  Generally  the  smudge  is  on  the  outside  scales, 
though  it  may  appear  on  the  inner  scales  as  well.  It  should 
not  be  confused  with  the  black  powder  which  is  character- 
istic of  black  mold. 

It  is  of  widespread  geographic  distribution,  but  only  white 
varieties  are  seriously  affected.  Infection  takes  place  in 
the  field  from  the  fungus  which  overwinters  in  the  soil.  The 
disease  appears  shortly  before  the  harvest,  and  develops 
rapidly  in  the  crated  onions  after  the  harvest  if  the  weather 
is  moist.  It  causes  very  little  shrinkage  of  affected  bulbs, 
the  chief  damage  being  due  to  the  appearance  and  reduced 
market  value  of  affected  bulbs. 

Smudge  can  be  prevented  by  rapid  curing  of  the  crop  as 
soon  as  it  is  harvested.  If  the  bulbs  are  stored  in  a  dry  place, 
the  disease  makes  little  progress.  In  a  moist  atmosphere, 
the  fungus  penetrates  from  scale  to  scale,  and  causes  a  soft- 
ening of  the  tissues. 

Ref.  (72). 

ONION:     SMUT. 

Cause:    A  fungus  (Urocystis  cepulae). 

Onion  smut  appears  as  dark-colored,  slightly  raised 
streaks  or  blisters  on  the  bulbs  and  leaves.  The  leaves  are 
often  recurved  and  distorted.  Sets  may  be  greatly  shrunken 
with  the  whole  exterior  covered  with  the  blisters.  When  cut 
open,  these  ridges  or  pustules  are  found  to  be  filled  with  a 
greenish  black  powdery  mass.  Smut  differs  from  black  mold 
in  that  the  black  powder  is  within  the  tissues  of  the  scale, 
not  upon  or  between  the  scales. 


MARKET  DISEASES  OF  VEGETABLES.  41 

Onion  smut  is  common  in  northern  growing  regions,  espe- 
cially in  Wisconsin,  Illinois,  New  York,  Ohio,  Iowa,  and 
Massachusetts. 

The  fungus  persists  in  the  soil,  and  infection  occurs  when 
the  plants  are  seedlings.  Badly  infected  plants  are  usually 
killed  and  large  losses  are  thus  caused  in  the  field.  There 
is  no  progress  of  the  disease  in  storage  or  transit.  Smut  is 
uncommon  in  the  market  except  on  onion  sets. 

Control  measures  are  planting  in  clean  soil  or  the  use  of  a 
formaldehyde  drip  on  the  seed  drill. 

Ref.  (71). 

ONION:     MISCELLANEOUS    DISEASES. 

BLOTCH. 

Cause:     A  fungus  (Macrosporium). 

The  name  "blotch"  has  been  temporarily  adopted  for  this 
blemish  on  the  outer  scales  of  red  and  yellow  varieties  of 
onions.  The  symptoms  are  large  bleached  or  greenish  dis- 
colored areas  on  the  bulbs,  bearing  numerous  fine  black 
linear  marks  or  ridges  parallel  to  the  veins. 

BLUE    MOLD. 

Cause:    A  fungus  (Penicillium). 

Under  certain  conditions  in  storage  or  transit,  blue  mold 
occurs  on  the  outside  of  the  bulbs,  and  is  usually  associated 
with  insufficient  ventilation  and  some  predisposing  injury  to 
the  tissues,  such  as  wounds,  freezing,  or  sun-scald. 

While  most  fruits  are  subject  to  attack  by  species  of  Peni- 
cillium, among  vegetables,  only  onions,  sweet  potatoes  and 
sweet  corn  are  commonly  attacked. 

FUSARIUM    ROT. 

Cause:     A  fungus  (Fusarium). 

This  rot  usually  but  not  always  proceeds  from  the  base 
of  the  bulb.  The  affected  region  is  soft  and  flabby  and  be- 
comes shrunken  and  shriveled  in  appearance.  The  surface 
may  be  studded  with  small  white  pads,  the  fruiting  bodies 
of  the  causal  fungus.  There  is  no  development  of  gray  mold 
or  black  sclerotia  as  in  neck  rot. 

GRAY    MOLD    SPOT. 

Cause:    A  fungus  (Botrytis). 

This  disease  causes  a  bright  red  lesion  on  the  neck  at  the 
ground  line,  which  results  in  the  death  of  the  outer  leaf.  At 
times  a  slight  outgrowth  of  gray  mold  may  be  formed  in  the 
lighter  colored  center  of  the  lesion.  Gray  mold  spot  is  found 
only  on  winter-grown  green  onions  in  the  spring,  and  has 
been  noted  in  the  Kansas  City  market  gardens. 

SUN-SCALD. 
(See  Sim-Scald). 


42  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

PARSNIP:    GRAY    MOLD    ROT;    BOTRYTIS    ROT. 

(See  Gray  Mold  Rot). 

PARSNIP:    WATERY    SOFT    ROT;    SCLEROTINIA    ROT. 

(See  Watery  Soft  Rot). 

PEA:     BACTERIAL   SPOT. 

Cause :    Bacteria. 

On  the  pods  this  disease  appears  as  greasy  water-soaked 
spots  which  may  enlarge  to  irregularly  circular,  slightly 
sunken  watersoaked  blotches  with  gray  centers. 

This  is  a  rather  widespread  disease  of  the  vines,  and  pod 
infection  occurs  in  the  field.  It  seems  likely  that  the  spots 
enlarge  during  transit.  Bacterial  spot  was  found  commonly 
in  the  Chicago  market  in  the  summer  of  1918,  and  appeared 
to  predispose  the  stock  to  secondary  rots. 

No  control  is  known  at  present. 

PEA:     POD    SPOT. 

Cause:    A  fungus  (Ascochyta  pisi). 

The  symptoms  of  this  disease  are  rather  small,  definitely 
circular  and  sharply  depressed  spots  with  tan-colored  or 
pinkish  centers  often  bearing  small  pimples,  the  pycnidia  of 
the  fungus. 

This  is  a  serious  field  disease  affecting  the  leaves  and 
stems  as  well  as  the  pods.  Pod  infection  occurs  in  the  field, 
and  there  is  probably  little  spread  of  the  disease  during 
transit. 

Control  involves  crop  rotation  and  the  use  of  disease-free 
seed. 

Ref.  (73). 

PEA:    SLIMY    SOFT    ROT;    BACTERIAL    ROT. 

(See  Slimy  Soft  Rot). 

PEA:    WATERY    SOFT    ROT;    SCLEROTINIA    ROT. 

(See  Watery  Soft  Rot). 

PEPPER:    ANTHRACNOSE. 

Cause:    A  fungus  (Gloeosporium). 

Slate-colored  to  charry  black,  sunken  lesions  are  char- 
acteristic of  this  disease.  The  margins  of  the  lesions  either 
are  darker  colored  or  watersoaked  but  of  the  same  color  as 
the  healthy  tissue,  and  wrinkled.  Under  moist  conditions 
salmon-colored  dots  or  spore  heaps  occur,  which  may  run 
together  and  form  a  slimy  mass.  These  dots  are  the  acer- 
vuli  (sing,  acervulus)  of  the  fungus  and  furnish  a  positive 
diagnostic  character  for  this  disease. 

This  disease  is  found  frequently  on  peppers.  Very  fre- 
quently, under  market  conditions,  the  lesions  do  not  bear 


MARKET  DISEASES  OF  VEGETABLES.  43 

cicervuli  but  become  covered  with  a  black,  velvety  growth  of 
Alternaria  species. 

PEPPER:    RHIZOPUS    ROT. 

(See  Rhizopus  Rot). 

PEPPER:  SLIMY  SOFT  ROT;  BACTERIAL  ROT. 

(See  Slimy  Sjft  Rot). 

PEPPER:    WATERY   SOFT    ROT;    SCLEROTINIA    ROT. 

(See  Watery  Soft  Rot). 

PEPPER:    SUN-SCALD. 

(See  Sun-Scald). 

POTATO:     BLACK    SCURF    AND    RUSSET    SCAB. 

.    Cause:    A  fungus  (Rhizoctonia). 

Black  scurf  and  russet  scab  are  skin  diseases.  Affected 
potatoes  are  rough  and  dirty  in  appearance,  or  may  have  a 
cracked  or  corroded  skin.  Both  are  field  diseases  caused  by 
the  same  fungus. 

Black  scurf  is  characterized  by  the  presence  of  small 
brown  or  black  masses  or  sclerotia  on  the  tuber,  often  re- 
ferred to  as  "dirt  which  will  not  rub  off."  These  masses 
may  be  circular  or  irregular  in  outline  and  single  or  joined 
into  series.  Washing  the  tuber  brings  these  into  sharp  relief. 

Russet  scab  is  a  corrosion  of  the  tuber  skin.  In  some  cases 
smooth-skinned  tubers  show  local  or  general  netting,  either 
slight,  or  so  extensive  as  to  resemble  the  skin  of  netted  varie- 
ties. In  advanced  stages  the  corrosion  becomes  channeled, 
and  the  intersecting  channels  may  become  so  deep  that  the 
tuber  surface  suggests  alligator  hide. 

In  many  cases,  tubers  are  literally  covered  with  black 
scurf  without  any  apparent  russeting,  while  in  other  cases 
the  presence  of  the  fungus  seems  to  cause  only  a  cracking 
or  scabbing,  without  any  sclerotia. 

Generally  neither  black  scurf  nor  russet  scab  are  serious 
enough  to  affect  the  market  value  of  potatoes.  The  former 
occasionally  is  severe  enough  to  affect  the  appearance  of  the 
tuber.  At  times,  in  very  moist  cars  or  storage  places,  the 
sclerotia  germinate,  and  the  potatoes  become  covered  with 
a  luxuriant  growth  of  mold  which  detracts  from  the  good 
appearance  of  the  lot.  Russet  scab,  however,  affects  the 
appearance  of  the  tuber  more  markedly,  and  often  corrodes 
the  skin  suffciently  to  necessitate  deep  paring,  which  is 
attended  by  a  waste  of  food. 

Ref.  (50);  (64). 

POTATO:      SILVER    SCURF. 

Cause:     A  fungus  (Spondylocladium  atrovirens). 


44  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

Silver  scurf  is  a  skin  disease  which  is  purely  superficial, 
and  does  not  penetrate  below  the  cork  layer.  The  infected 
areas  are  marked  by  their  silvery  appearance,  which  is  espe- 
cially pronounced  if  the  tubers  are  washed.  In  late  stages 
of  the  disease,  the  affected  skin  becomes  wrinkled  and 
sloughs  off. 

Generally,  affected  areas  occur  near  the  stem  end,  but 
they  may  be  found  over  the  entire  surface.  Diseased  areas 
vary  from  one-fourth  inch  to  one  inch  or  more  in  diameter. 

In  storage,  especially  under  moist  conditions,  a  sooty  layer 
composed  of  the  spores  of  the  fungus  may  be  found  on  the 
diseased  areas. 

Infected  stock  is  fit  for  table  use. 

Ref.  (43);  (57). 

POTATO:     WART. 

Cause:    A  fungus  (Chrysophlyctis  endobiotica). 

In  its  early  stages,  wart  is  characterized  by  small,  warty 
outgrowths  which  usually  occur  at  the  eyes  of  the  tuber. 
These  warts  later  become  very  large,  and  in  severe  cases, 
cover  or  involve  the  entire  tuber.  They  are  rough  and  black 
in  color. 

This  disease  is  serious  in  certain  parts  of  Europe,  and  has 
recently  made  its  appearance  in  the  United  States  (Penn- 
sylvania). It  is  a  very  destructive  field  disease,  and  may  be 
carried  with  diseased  seed  tubers.  Once  having  gained  a 
foothold,  the  fungus  persists  for  long  periods  in  the  soil. 

Infection  takes  place  in  the  field  while  the  tubers  are 
growing.  The  disease  does  not  progress  in  storage,  and  does 
not  spread  to  healthy  tubers.  Diseased  stock  is  very  subject 
to  secondary  rots,  and  in  this  way  it  is  a  menace  to  healthy 
stock.  Slightly  affected  tubers  may  be  used  for  table 
purposes. 

Precaution  against  the  use  of  diseased  tubers  for  seed 
purposes  is  of  prime  importance  in  the  prevention  of  this 
disease.  With  this  end  in  view  a  National  quarantine  has 
been  established. 

Ref.  (35);  (63). 

POTATO:     COMMON    SCAB. 

Cause:    A  fungus  (Actinomyces  scabies). 

Scab  is  characterized  by  rough  corky  elevations,  or  by 
pits.  If  tubers  are  attacked  early,  the  pits  are  deep ;  if  late, 
they  may  be  shallow  and  superficial.  In  the  early  stages, 
affected  tubers  are  marked  with  minute,  reddish  or  brown- 
ish surface  lesions.  Cork  formation  usually  occurs  under- 
neath these  lesions.  Often  the  lesions  coalesce  and  in  severe 
cases  the  entire  tuber  may  be  covered  by  a  rough  incrusta- 
tion. Scabby  potatoes  are  little  if  any  more  disposed  to 
decay  than  clean  potatoes. 


MARKET  DISEASES  OF  VEGETABLES.  45 

Deep  scab  is  an  advanced  stage  of  common  scab.  Often 
insects  or  mites  live  in  scab  pockets.  It  is  not  known  to  just 
what  extent  these  are  responsible  for  the  Lesions. 

Common  scab  occurs  in  all  varieties  of  potatoes  and  is 
most  common  in  potatoes  grown  in  alkaline  soil.  Treatment 
of  seed  stock  with  corrosive  sublimate,  and  planting  in  unin- 
fected  soil  or  acid  soil  are  fair  preventives  of  the  trouble. 

Wire  worm  or  grub  injury  often  are  confused  with  scab 
lesions.  It  frequently  is  difficult  to  differentiate  between 
them.  Wireworm  injury  is  generally  marked  by  extensive 
channeling  in  the  tuber  skin,  while  grub  injury  is  marked  by 
deep,  broad  pits  with  protruding  or  overhanging  rims.  Wire- 
worm  and  grub  injuries  often  are  points  of  entry  for  Fusa- 
rium  species. 

Scab  and  insect  injuries  depreciate  the  value  of  tubers 
for  table  use  by  making  them  unsightly,  and  by  necessitat- 
ing deep  paring  with  attendant  loss  of  food. 

Ref.  (10);  (38);  (39);  (50). 

POTATO:     POWDERY    SCAB. 

Cause:    A  slime  mold  (Spongospora  subterranea). 

In  the  early  stages  powdery  scab  consists  of  pimple  or 
blister-like  eruptions,  one-sixteenth  to  one-quarter  inch  in 
diameter,  which  are  completely  covered  by  the  skin  of  the 
tuber.  Later  these  coverings  rupture  and  expose  pits,  which 
are  single  or  joined,  and  fringed  by  the  flaring,  papery, 
torn,  and  more  or  less  toothed  remnants  of  the  skin.  The 
interior  of  these  pits  is  at  first  filled  with  a  brown  powder 
or  dust,  which  is  usually  absent  when  the  tubers  reach  mar- 
ket. Often  the  tissues  surrounding  the  pits  become  discol- 
ored and  sunken,  and  each  pit  or  group  of  pits  appears  as  a 
crater  in  a  sunken  zone. 

Powdery  scab  differs  from  common  scab  in  the  more 
nearly  circular  lesions,  smaller  pits,  presence  of  brown  dust, 
star-like  rupture  of  the  skin,  and  relative  absence  of  cork 
formation. 

This  disease  is  not  as  serious  a  menace  as  it  was  once 
thought  to  be.  It  seems  to  be  localized  in  a  few  sections  of 
North  America,  and  is  causing  little  damage.  It  is  favored 
by  cool,  moist  weather. 

The  causal  organism  is  introduced  into  the  soil  with  dis- 
eased seed  stock,  and  tuber  infection  occurs  in  the  field. 

Affected  stock  is  fit  for  table  use.  Its  market  value,  how- 
ever, is  decreased  because  of  its  unsightliness,  and  because 
of  the  waste  due  to  deep  paring. 

Ref.  (44);  (46). 

POTATO:     LATE    BLIGHT    TUBER    ROT. 

Cause:    A  fungus  (Phytophthora  infestans). 

Late  blight  tuber  rot  is  characterized  externally  by  de- 
pressed, discolored  areas  of  irregular  but  definite  outline. 
These  may  occur  merely  as  spots  or  as  very  extensive  lesions. 


46  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

The  affected  areas  often  have  a  metallic  or  purplish  tinge 
which  is  especially  marked  at  the  margin  where  the  dis- 
eased tissue  joins  the  healthy.  At  times,  a  pinkish  color  is 
apparent  when  the  outer  skin  of  affected  areas  is  first  re- 
moved. The  diseased  tissues  underlying  the  sunken  areas 
are  browned,  and  unless  secondary  rots  have  set  in,  are  quite 
dry  and  firm.  The  tissue  is  merely  killed,  not  disintegrated. 
In  cross  section  it  is  seen  that  the  affected  tissue  tends  to  be 
limited  to  the  outer  parts  of  the  tuber,  and  that  the  advanc- 
ing edge  is  irregular  and  feathery. 

Under  storage  conditions,  especially  if  the  air  is  very 
moist,  secondary  rots  due  to  bacteria  or  fungi  set  in.  At 
times,  in  advanced  cases,  it  is  difficult  to  ascertain  whether 
the  primary  cause  of  rotting  was  freezing  injury,  with  sub- 
sequent bacterial  and  fungous  infection,  or  late  blight.  In 
such  cases  the  deciding  factors  are  the  presence  in  the  ship- 
ment of  clear-cut  cases  of  late  blight  or  of  freezing  injury. 

Potatoes  affected  with  late  blight  do  not  show  the  hollow 
brittle  regions  found  in  potatoes  affected  with  Fusarium 
tuber  rot,  nor  the  shriveled  and  wrinkled  surfaces  caused  by 
Fusarium  or  freezing  injury.  The  feathery  edge  of  the 
tissue  killed  by  the  late  blight  fungus  also  serves  to  differ- 
entiate it  from  tissues  killed  by  Fusarium  or  freezing. 

Late  blight  tuber  rot  occurs  most  commonly  in  potatoes 
grown  in  the  Eastern  and  North  Central  States,  and  in  the 
coastal  portions  of  the  Pacific  Northwest  States.  Under  cer- 
tain weather  conditions,  it  also  occurs  in  southern  potatoes. 
During  the  rainy  season  of  1918,  late  blight  was  prevalent 
in  Florida  potatoes.  It  is  not  a  hot  weather  disease  but  is 
favored  by  cool,  wet  weather. 

Late  blight  is  one  of  the  most  important  field  diseases  of 
the  potato,  causing  a  severe  blight  of  the  vines  in  addition 
to  its  attack  on  the  tubers. 

The  fungus  overwinters  in  diseased  tubers,  and  is  intro- 
duced into  the  field  with  diseased  seed  stock.  From  dis- 
eased seedlings  produced  by  such  seed,  the  fungus  spreads 
rapidly  throughout  the  field  when  weather  conditions  are 
favorable.  Tubers  are  infected  in  the  field  by  spores  washed 
down  or  spattered  from  the  diseased  vines.  The  disease 
also  develops  in  transit  and  storage. 

Late  blight  can  be  controlled  in  the  field  by  spraying  with 
Bordeaux  mixture.  Its  development  in  transit  and  storage 
is  checked  by  a  dry  atmosphere  and  a  low  temperature  (34° 
to  36°  F.;  45°  F.  is  too  warm).  It  is  highly  desirable  that 
diseased  tubers  be  sorted  out  as  soon  as  they  can  be  de- 
tected. In  case  of  a  late  blight  epidemic,  digging  should  be 
postponed  until  the  tops  have  dried  up. 

Affected  tubers  are  not  marketable  for  table  use.  They 
are  also  a  menace  to  sound  stock  in  transit  and  storage  since 
secondary  rots,  such  as  Fusarium  or  slimy  soft  rot,  very  fre- 
quently follow  late  blight. 

Ref.  (9);  (18);  (34);  (45). 


MARKET  DISEASES  OF  VEGETABLES.  47 

POTATO:     FUSARIUM    TUBER   ROT. 

Cause:    Fungi  (Fusarium  species) . 

Fusarium  tuber  rot  is  generally  marked  by  sunken,  shriv- 
eled, wrinkled,  or  broken  areas*  on  the  tuber  surface.  These 
areas  may  be  brown  to  black  in  color  and  on  them  may 
appear  masses  of  whitish  or  brightly  colored  mold. 

The  diseased  tissue  underlying  such  discolored  and 
shrunken  areas  may  be  dry  and  brittle,  and  may  contain 
cavities  lined  with  a  white  or  bright  colored  growth  of  the 
fungus  responsible  for  the  rot;  or  this  tissue  may  be  watery 
but  intact,  depending  upon  the  species  of  fungus  responsible 
for  the  rot  and  the  conditions  under  which  the  affected  tuber 
was  kept.  Usually,  if  affected  tubers  are  kept  in  a  dry  cool 
place,  the  dry,  brittle,  and  hollow  type  of  powdery  dry  rot 
results.  If  they  are  kept  in  a  warm  moist  place  the  soft 
intact  type  of  rot  is  usually  the  result.  Affected  tissue  may 
be  gray  or  brown  to  black  in  color. 

The  rot  may  proceed  from  the  stem  or  seed  end,  from  the 
eyes  or  from  broken  places  in  the  skin,  such  as  cuts  and 
bruises.  At  times  the  infection  is  confined  to  a  mere  dis- 
coloration of  the  vascular  ring  proceeding  from  the  stem 
end  of  the  tuber.  This  is  not  visible  until  the  tuber  is  cut. 
This  discoloration  cannot  always  be  positively  differenti- 
ated, without  miscroscopic  examination  and  cultural  test, 
from  discolprations  due  to  freezing  injury  or  to  varietal 
characteristics.  Fusarium  discoloration  penetrates  much 
farther  into  the  tuber,  however,  than  other  vascular  dis- 
coloration. In  southern  potatoes,  this  discoloration  in  the 
ring  can  be  told  from  a  similar  discoloration  due  to  brown 
rot  by  the  absence  of  the  slimy  bacterial  masses  or  droplets 
which  ooze  out  when  tubers  affected  with  brown  rot  are  cut. 

This  stem-end  infection  and  some  lenticel  and  eye  infec- 
tions occur  in  the  field.  Stem-end  invasion  is  very  common 
in  potatoes  produced  by  plants  affected  with  Fusarium  wilt. 
Jelly-end  is  another  type  of  stem-end  infection  which  occurs 
in  the  field.  However,  most  of  the  tubers  rotted  by  Fusa- 
rium species  are  infected  through  breaks  in  the  skin  caused 
during  and  after  the  harvest. 

Tubers  with  areas  injured  or  killed  by  freezing  are  very 
subject  to  Fusarium  rots.  The  rot  usually  starts  in  at  some 
point  which  did  not  heal  over  completely  with  cork  or  was 
not  entirely  sealed  with  starch  following  the  drying  out  of 
the  frozen  tissue.  At  times  it  is  very  difficult  to  distinguish 
between  potatoes  with  frozen  areas  which  were  subse- 
quently infected  with  Fusarium  tuber  rot,  and  potatoes 
which  were  originally  affected  with  the  rot  and  then  kept 
under  moist  conditions.  The  end  result  in  both  cases  is 
usually  a  wet  brown  rot.  This  wet  type  of  rot  is  especially 
marked  in  the  Burbank  and  Netted  Gem  potatoes  from 
Idaho.  It  may  be  practically  impossible  at  times  to  deter- 
mine the  cause  of  the  decay  by  examination  of  a  single  tuber 


48  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

without  a  microscopic  examination  or  cultural  test.  An 
examination  of  the  entire  lot,  however,  will  reveal  the  pres- 
ence or  absence  of  typical  signs  of  freezing  injury.  The 
frozen  tissue  of  a  tuber  usually  is  set  off  from  the  healthy 
tissue  by  a  more  or  less  straight  purple  or  brown  line  which 
extends  across  all  the  tissues  of  the  tuber,  or  by  a  gray, 
chalky,  brittle  layer  of  starch.  On  the  other  hand,  most 
Fusarium  species  generally  tend  to  rot  the  center -of  the 
tuber  faster  than  the  cortical  tissue,  leaving  a  shell  of  sound 
tissue  enclosing  a  rotted  center. 

An  examination  of  the  surface  of  a  tuber  may  not  be  suf- 
ficient to  determine  whether  the  tuber  is  affected*  with  late 
blight  or  Fusarium  tuber  rot.  Both  produce  sunken  dis- 
colored areas.  The  late  blight  tuber  rot,  however,  causes 
more  of  a  metallic  luster  than  the  Fusarium  tuber  rot,  and 
usually  the  sunken  area  is  not  shrunken  and  shriveled.  In 
tubers  affected  with  late  blight,  the  diseased  tissues  under- 
lying the  discolored  areas  are  solid  and  dry  and  have  a 
feathery  edge,  while  in  the  Fusarium  tuber  rot  the  diseased 
tissue,  if  dry,  contains  cavities  or  is  watery  and  soft  and  in 
cross-section  is  set  off  from  healthy  tissue  by  a  sharp,  smooth 
edge. 

Tubers  affected  with  the  soft,  wet,  brown  type  of  Fusa- 
rium tuber  rot  can  be  differentiated  from  tubers  affected 
with  the  slimy  soft  rot  by  the  absence  of  the  foul  odor  so 
characteristic  of  all  bacterial  soft  rots.  Fusarium-infected 
tissue  is  not  slimy  even  though  it  is  soft  and  disintegrated. 

Deterioration  of  tubers  due  to  Fusarium  tuber  rot  is  some- 
times rapid  and  often  complete.  Infected  tubers  are  a  men- 
ace to  healthy  ones.  Immature  tubers,  cut  and  bruised 
tubers,  tubers  with  second  growth  knobs  which  are  easily 
broken  off,  tubers  affected  with  other  diseases  such  as  late 
blight  tuber  rot  or  blackleg,  and  tubers  with  frozen  areas 
are  an  easy  prey  for  the  Fusarium  species  causing  tuber  rot. 

One  or  more  forms  of  Fusarium  tuber  rot  occur  in  practi- 
cally all  potato  districts.  Fusarium  tuber  rot  is  much  more 
common  in  northern  than  in  southern  potatoes.  It  does 
develop,  however,  in  southern  potatoes  shipped  north  and 
causes  a  very  soft,  watery  rot  or  a  stem-end  rot.  The  orig- 
inal infection  may  occur  in  the  field,  in  transit  or  in  storage, 
but  in  most  cases  the  rot  develops  and  spreads  in  transit  and 
storage.  In  a  few  cases,  such  as  jelly-end  rot  and  black  field 
rot,  the  disease  develops  in  the  field. 

The  Fusarium  tuber  rot  in  potatoes  from  the  Central 
Western  States,  especially  in  the  Early  Ohio  stock  from 
Nebraska  and  Minnesota,  and  the  Burbank  and  Netted  Gem 
stock  from  Idaho,  is  called  powdery  dry  rot.  This  term 
refers  more  to  the  appearance  of  the  spore  masses  of  the 
fungus  than  to  the  diseased  tuber  tissues.  The  Fusarium 
tuber  rot  in  potatoes  from  the  Eastern  States  is  designated 
as  tuber  rot  or  dry  rot  and  generally  is  of  the  wet  type.  The 


MARKET  DISEASES  OF  VEGETABLES.  49 

Fusarium  tuber  rot  appearing  at  the  end  of  the  tuber  in  the 
long,  white  varieties  of  the  Northwest,  such  as  the  Burbank, 
is  known  as  jelly-end,  while  that  appearing  in  other  parts  of 
the  tuber,  especially  marked  in  the  round  varieties  such  as 
the  Rural,  is  known  as  "black  field  rot."  These  rots  are 
caused  by  Fusarium  radicicola,  which  also  causes  a  very  soft 
leaky  rot  and  a  dry,  black  stem-end  rot  of  potatoes  grown 
in  the  southern  half  of  the  Mississippi  Valley. 

Wounded  or  bruised  surfaces  which  have  become  sealed 
with  starch  or  cork  should  not  be  confused  with  Fusarium 
infections.  Generally  tuber  rot  starts  in  bruises  and  cuts. 
During  the  early  storage  season,  it  is  often  impossible  to 
determine  whether  or  not  a  bruise  or  cut  will  develop  tuber 
rot.  Later  in  the  season  the  presence  of  soft  discolored 
tissue  or  cavities  lined  with  mycelium  makes  a  diagnosis 
much  easier. 

The  safest  and  surest  methods  of  control  are  careful  han- 
dling of  tubers  to  avoid  cutting  and  bruising;  sorting  out  of 
bruised,  broken,  cut,  diseased,  and  frozen  potatoes;  and 
storing  of  tubers  in  a  well-ventilated  place  at  a  temperature 
between  36°  and  40°  F. 

Ref.  (7);  (37). 

POTATO:     JELLY   END    ROT;    BLACK   FIELD    ROT. 

Cause:    A  fungus  (Fusarium  radicicola). 

Both  jelly  end  and  black  field  rot  are  types  of  the  Fusa- 
rium tuber  rot  previously  described.  In  jelly  end  rot,  the 
end  of  the  tuber  is  shrunken  and  collapsed,  while  black  field 
rot  is  characterized  by  shrunken,  collapsed,  black  to  brown 
areas  occurring  anywhere  on  the  surface  of  the  tuber. 

The  diseased  tissue  underlying  the  discolored  or  shrunken 
surface  is  soft,  watery,  and  light  to  dark  brown  or  black  in 
color,  or  it  may  be  rather  firm  and  black.  Unlike  powdery 
dry  rot,  cavities  generally  do  not  occur  in  the  affected 
tissues. 

The  moist  condition  of  jelly  end  rot  is  not  observed  unless 
the  potatoes  have  just  been  dug  or  have  been  removed  re- 
cently from  a  car  which  sweated  or  became  overheated  in 
transit.  Generally,  under  market  conditions,  the  disinte- 
grated tissue  dries  out  and  resembles  typical  dry  rot.  Very 
often  stock  affected  initially  with  jelly  end  or  black  field  rot 
subsequently  becomes  affected  with  powdery  dry  rot,  which 
progresses  rapidly  in  storage. 

These  rots  occur  most  commonly  in  Nebraska,  Idaho,  and 
Pacific  Coast  potatoes.  Jelly  end  rot  is  prevalent  in  the  long 
varieties  such  as  the  Burkbank  type,  while  black  field  rot  is 
most  clearly  marked  in  the  round  varieties  such  as  the 
Rural.  Without  a  cultural  examination  it  is  impossible  to 
differentiate  at  times  between  jelly  end  rot  and  so-called 
dry  rot  of  the  end  of  the  tuber  caused  by  Fusarium  species 
other  than  Fusarium  radicicola. 


50  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

The  original  infection  takes  place  in  the  field.  Both  dis- 
eases develop  in  the  field.  They  probably  do  not  develop  or 
spread  in  transit  and  storage,  but  do  open  the  way  for  other 
Fusarium  tuber  rots. 

Fusarium  radicicola  may  cause  in  southern  potatoes  a  very 
watery  leaky  rot  which  involves  the  entire  tuber  and  re- 
sembles the  watery  soft  rot  of  other  vegetables  caused  by 
Sclerotinia.  This  rot  differs  from  jelly  end  and  black  rot 
in  that  the  whole  tuber  is  affected  and  that  the  rot  is  watery 
rather  than  jelly-like  or  firm.  The  diseased  tissue  is  only 
slightly  discolored.  Under  certain  conditions  in  transit,  an 
extensive  mycelial  growth  and  numerous  bodies  which  re- 
semble small  sclerotia  develop  on  the  surfaces  of  affected 
tubers. 

In  this  leaky  rot  of  southern-grown  potatoes  caused  by 
Fusarium  radicicola,  the  original  infection  takes  place  in  the 
field.  This  type  of  rot  is  favored  by  hot  weather,  and  is  very 
frequently  associated  with  scald.  It  is  probable  that  this 
disease,  unlike  jelly  end  or  black  field  rot,  develops  and 
spreads  rapidly  in  transit. 

Ref.  (7);  (54). 

POTATO:     POWDERY   DRY    ROT. 

Cause :     A  fungus  (Fusarium  trichothecioides) . 

Powdery  dry  rot  is  a  type  of  the  Fusarium  tuber  rot  pre- 
viously discussed.  In  the  name  powdery  dry  rot,  the  word 
powdery  does  not  refer  to  the  appearance  of  the  diseased 
tissue  but  to  the  powdery  masses  of  spores  formed  by  this, 
fungus. 

In  this  disease  the  affected  region  contains  cavities  sepa- 
rated by  dried  brownish  tissue  and  starch  and  lined  with 
whitish  fluffy  mycelium  or  powdery  pink  masses  of  spores. 
In  the  early  stages,  the  affected  tissue  is  light  brown  to  black 
in  color  and  is  sharply  delimited  from  the  healthy  tissue  by 
a  layer  of  brown  or  black  tissue.  Affected  tubers  are  much 
lighter  in  weight  than  healthy  tubers  because  of  the  exten- 
sive hollow  areas.  This  rot  is  most  pronounced  in  the  cen- 
tral portion  of  the  tuber,  and  as  a  result,  affected  tubers 
often  become  more  or  less  hollow  shells. 

If  tubers  infected  with  powdery  dry  rot  are  stored  in  a 
very  moist  atmosphere,  or  if  they  become  infected  with  bac- 
teria, the  typical  symptoms  are  partly  masked  by  the  pres- 
ence of  soft  watery  tissues  of  chocolate  color,  which  gener- 
ally are  more  extensive  than  the  typical  dry  areas. 

Potatoes  just  taken  from  a  car  which  has  been  in  transit  a 
long  time,  or  which  was  not  cooled  or  ventilated  properly, 
show  the  symptoms  of  wet  Fusarium  rot  rather  than  the 
symptoms  of  powdery  dry  rot.  However,  upon  exposure  to 
the  air  the  typical  dry  rot  symptoms  soon  develop. 

Powdery  dry  rot  appears  to  progress  more  rapidly  at 
lower  temperatures  than  the  other  Fusarium  tuber  rots.  It 
occurs  mainly  in  Idaho  and  other  Rocky  Mountain  districts, 


MARKET  DISEASES  OF  VEGETABLES.  51 

and  in  western  Nebraska,  being  especially  severe  in  the 
Early  Ohio  variety.  It  is  prevalent  in  bruised  or  frozen 
potatoes  from  Washington,  Idaho,  Nebraska  and  Colorado. 

Infection  takes  place  through  breaks  in  the  skin  of  the 
tuber.  These  may  be  brought  about  by  cuts  or  bruises,  by 
freezing  and  by  attacks  of  other  fungi.  The  spores  of  Fusa- 
rium  are  usually  everywhere  present  in  the  soil,  on  the  sur- 
faces of  tubers,  and  in  storage  places,  so  that  any  break  in 
the  tuber  skin  is  very  likely  to  become  infected. 

Control  of  this  disease  depends  upon  careful  handling  of 
potatoes  to  minimize  injury  as  far  as  possible.  Because  of 
the  rapid  progress  of  the  rot,  it  is  advisable  to  dispose  of 
affected  stock  at  the  earliest  opportunity.  It  is  not  profit- 
able to  ship  severely  affected  stock. 

Ref.  (37)  ;  (53). 

POTATO:     LEAK. 

Cause:  Fungi  (Pythium  debaryanum;  sometimes  Rhiz- 
opus  nigricans). 

Leak  is  marked  at  first  by  a  brown  discoloration  around 
wounds  or  bruised  areas.  The  discoloration  later  becomes 
extensive,  and  the  entire  interior  of  the  potato  may  become 
soft,  and  buff  or  light  brown  in  color.  Under  pressure,  the 
affected  tubers  exude  a  brownish  watery  liquid,  and  dis- 
eased tubers  often  leak  badly.  Potatoes  affected  with  leak 
are  much  more  watery  than  those  affected  with  the  wet  type 
of  Fusarium  tuber  rot. 

Leak  has  been  reported  only  from  the  Delta  lands  of  the 
San  Joaquin  Valley  of  California  and  from  Idaho.  It  does 
not  occur  in  cool  weather,  and  is  entirely  checked  by  heavy 
frosts. 

Infection  takes  place  in  the  field,  and  tubers  are  infected 
only  through  wounds,  such  as  those  due  to  fork  injury  or 
the  breaking  off  of  second-growth  knobs.  Infection  occurs 
only  in  hot  weather,  but  once  the  disease  has  gained  a  foot- 
hold, it  may  devevlop  at  lower  temperatures. 

Leak  can  be  controlled  by  careful  digging  and  handling 
of  the  potatoes  and  sorting  out  of  bruised  and  broken  tubers. 
In  addition  it  has  been  found  advisable  to  hold  suspected 
potatoes  4  days  in  the  warehouse  before  shipment  so  that 
the  disease,  if  present,  may  develop  and  be  more  readily 
detected.  It  is  not  likely  to  be  a  storage  trouble  after  the 
warm  season. 

Ref.  (28);  (29). 

POTATO:  BROWN  ROT  (SOUTHERN  BACTERIAL  WILT). 

Cause:     Bacteria  (Bacillus  solanacearum). 

Brown  rot  may  be  indicated  externally  by  a  slight  depres- 
sion at  the  point  of  attachment  of  the  stolon  to  the  tuber,  or 
by  gray  discolored  patches  on  the  surface.  Sometimes  no 
external  symptoms  may  be  visible.  Upon  cutting  infected 
tubers,  a  moist  brown  discoloration  and  slight  softening  of 


52  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

the  ring  (vascular)  tissue  of  the  tuber  is  seen.  White  sticky 
globules  of  bacteria  ooze  out  from  the  cut  tissues.  In  this 
stage,  the  rot  is  odorless. 

The  rot  begins  in  the  vascular  ring,  causing  cavities  which 
are  filled  with  a  dirty  white,  slimy,  bacterial  mass.  Brown 
rot  may  be  followed  by  slimy  soft  rot  to  which  the  foul  odor 
of  affected  tubers  is  due. 

This  rot  should  not  be  confused  with  the  ring  discolora- 
tion associated  with  Fusarium  wilt.  The  latter  is  most 
common  in  northern  potatoes,  while  brown  rot  occurs  only 
in  southern,  especially  Florida,  stock.  There  is  no  bacterial 
exudate  from  the  bundles  when  a  Fusarium  infected  tuber 
is  cut. 

Infection  takes  place  in  the  field  and  the  disease  is  there 
known  as  bacterial  wilt.  The  infection  proceeds  from  the 
affected  plant  through  the  horizontal  underground  stems 
(stolons)  into  the  tubers  which  are  enlargements  of  the 
stolons.  Potatoes  grown  in  new  soil  are  most  severely 
affected. 

It  is  advisable  not  to  plant  potatoes  in  new  ground.  In- 
fected stock  is  subject  to  decay  and  should  be  rapidly  dis- 
posed of. 

Ref.  (61). 

POTATO:     SLIMY    SOFT    ROT. 

Cause:    Bacteria  (Bacillus  carotovorus  group). 

This  disease  of  the  potato  belongs  to  the  class  of  slimy 
soft  rots  described  elsewhere,  but,  since  it  presents  itself  as 
a  special  phase  in  southern  potatoes,  a  separate  discussion 
is  warranted.  It  is  a  soft,  soupy,  exceedingly  foul  smelling 
rot.  Unless  affected  tissue  is  discolored  by  other  causes, 
there  is  little  change  in  color,  the  disintegrated  tissue  being 
whitish  to  yellow.  The  boundary  between  the  soft  disinte- 
grated and  the  firm  sound  tissue  is  very  sharp.  As  the  more 
or  less  watery  tissue  dries,  it  becomes  slimy  and  finally, 
when  completely  dry,  a  mere  chalky  white  crust.  During 
shipment  the  skin  of  affected  areas  is  broken  easily,  and  the 
slime  commonly  is  smeared  over  neighboring  sound  tubers. 
In  car-lot  shipments  this  very  materially  increases  the  diffi- 
culty of  sorting. 

Slimy  soft  rot  very  generally  invades  killed  tissue.  In  a 
wet  soil,  tubers  often  become  asphyxiated,  and  the  bacteria 
enter  the  tuber  through  scab  wounds,  through  lenticels  (the 
breathing  pores  of  the  tuber) ,  through  broken  places  in  the 
skin,  or  through  diseased  stolons.  Infection  also  occurs  very 
generally  through  bruises  received  during  digging  and  han- 
dling. If  infected  tubers  are  dug  while  wet,  and  scalded  by 
exposure  to  the  hot  sun,  or  if  sacked  with  the  wet  soil  adher- 
ing, a  procedure  which  may  lead  to  heating  or  sweating,  the 
rot  may  progress  rapidly  from  the  surface  inward  through 
the  whole  tuber. 


MARKET  DISEASES  OF  VEGETABLES.  53 

Brown  rot  may  be  followed  by  slimy  soft  rot  as  a  result 
of  which  large  cavities  are  formed  in  the  interior  of  the 
tuber.  The  decayed  tissue  often  is  so  viscous  that  it  can  be 
pulled  like  very  soft  taffy. 

Slimy  soft  rot  is  prevalent  as  a  surface  rot  in  potatoes 
shipped  from  Florida,  Louisiana  and  Texas.  It  is  favored 
by  wet,  hot  conditions  in  the  field,  in  transit  or  in  storage. 
After  the  rot  has  once  started,  the  temperature  is  of  less 
importance  than  the  humidity.  This  rot  occurs  also  in 
northern  potatoes.  Tubers  affected  with  black-leg  or  with 
scald  or  freezing  injury  are  predisposed  to  slimy  soft  rot. 
In  fact,  slimy  soft  rot  commonly  follows  freezing  injury  if 
the  temperature  after  thawing  is  high  enough  to  permit  the 
growth  of  the  bacteria. 

The  control  measures  are  careful  sorting  of  stock  which 
has  been  subjected  to  unfavorable  conditions  before  it  is  put 
into  transit  or  storage,  and  improvement  of  handling  meth- 
ods to  avoid  wounds  and  scald.  The  rot  progresses  and 
spreads  very  rapidly  in  transit  and  storage,  but  can  be 
checked  by  rapid  drying  of  affected  stock. 

POTATO:  SURFACE  MOLD. 

Cause :    Various  fungi. 

Under  transit  or  storage  conditions,  potatoes  often  show 
a  superficial  development  of  mold  growth  which  is  abso- 
lutely non-injurious  to  the  tubers  except  as  it  affects  their 
appearance.  Various  fungi  are  concerned,  including  blue 
mold  and  Rhizoctonia,  and  their  growth  is  favored  by  the 
presence  of  moisture,  especially  the  juice  from  nearby 
frozen  or  rotted  tubers.  Wet,  dirty  tubers  and  cut  or  bruised 
areas  are  likely  to  become  covered  with  surface  molds. 

Surface  molds  are  objectionable  in  bulk  shipments  be- 
cause of  the  bad  appearance  of  the  stock. 

Proper  ventilation  to  dry  the  surfaces  of  the  potatoes  will 
aid  in  preventing  this  trouble. 

POTATO:  HOLLOW  HEART. 

Cause :     Rapid  growth. 

Hollow  heart  is  a  more  or  less  irregular  cavity  in  the 
center  of  the  tuber,  varying  in  size  and  often  lined  by  tissue 
which  is  browned  and  glassy. 

Hollow  heart  occurs  most  frequently  in  large,  coarse, 
rapid-growing  varieties,  particularly  when  these  are  grown 
in  very  fertile  soils.  It  also  is  common  in  red  varieties  grown 
in  the  sand  hills  region  of  Nebraska. 

Hollow  heart  and  black  heart  may  be  confused  since 
cavities  occasionally  develop  in  tubers  affected  with  black 
heart ;  but  these  differ  from  those  of  hollow  heart  by  their 
association  with  discolored  tissue. 

Usually  hollow  heart  cannot  be  detected  until  the  affected 
potatoes  are  cut.  It  does  not  affect  their  keeping  quality. 

Affected  stock  is  very  undesirable  for  table  use. 

Ref.  (49). 


54  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

POTATO:    GROWTH    CRACKS;    SECOND    GROWTH. 

Cause :    Unfavorable  growing  conditions. 

Second  growth  and  misshapen  tubers  are  marked  by  a 
development  of  knobs  on  the  tuber's  surface,  and  growth 
cracks  by  wide,  deep  fissures,  which  are  usually  covered 
with  the  normal  protective  cork  layer  of  the  tuber. 

These  malformations  occur  in  all  varieties  and  in  all  local- 
ities, but  are  most  pronounced  where  there  is  considerable 
fluctuation  in  the  water  supply  of  the  growing  crop. 

Second  growth  tissues  are  immature,  and  are  subject  to 
peeling,  bruising,  and  freezing  injury.  These  knobs  are 
often  broken  off,  opening  a  way  for  Fusarium  infection. 

Growth  cracks  ordinarily  are  not  subject  to  tuber  rot  in- 
fection, whereas  mechanical  injury  such  as  cuts,  splits,  and 
bruises,  which  are  due  to  careless  handling,  do  not  develop 
the  normal  layer  of  cork,  hence  become  infected  very 
readily. 

Tubers  showing  these  deformities  are  of  inferior  grade, 
since  a  considerable  waste  in  paring  is  necessitated. 

POTATO:      IMMATURITY. 

Cause :  Premature  death  of  vines  in  the  field,  or  prema- 
ture digging  of  the  crop. 

Immaturity  is  characterized  by  excessive  peeling  of  the 
skin,  by  a  greenish  tint  under  the  skin,  and  by  a  tendency 
to  excessive  wilting  and  flabbiness  during  transit  and 
storage. 

This  trouble  occurs  mainly  in  late  varieties  of  the  North 
and  in  southern  potatoes  dug  for  early  marketing. 

Immature  tubers  are  subject  to  bruising,  therefore  to 
Fusarium  tuber  rot  infection,  to  freezing  injury,  and  to 
excessive  shrinkage  if  they  are  shipped  in  overheated  cars. 
They  are  not  high  grade  stock  and  often  are  bitter  in  taste. 

POTATO:     NET    NECROSIS    AND    INTERNAL    BROWN    SPOT. 

Cause:  Unfavorable  field  conditions  (possibly  mosaic 
disease). 

Net  necrosis  is  characterized  by  fine,  extensive  brown 
streaks  which  follow  the  vascular  tissues  and  form  a  net- 
work. The  discoloration  begins  at  the  stem  end,  where  it  is 
often  localized ;  or,  in  later  stages,  it  may  extend  throughout 
the  whole  tuber.  The  discolored  tissues  are  dead. 

It  occurs  in  many  varieties,  and  is  favored  by  poor  soil 
conditions  and  by  hot  weather. 

Internal  brown  spot  is  marked  by  brown  or  yellow  re- 
gions of  dead  tissues  scattered  throughout  the  tuber.  The 
affected  regions  may  be  small  or  large,  even  one-half  inch 
in  diameter.  They  may  be  scarce  or  numerous,  and  are 
isolated  and  not  connected  as  in  net  necrosis. 

The  disease  occurs  in  all  varieties,  and  is  favored  by  an 
inadequate  water  supply  during  the  growing  period. 


MARKET  DISEASES  OF  VEGETABLES.  55 

Neither  net  necrosis  nor  internal  brown  spot  should  be 
confused  with  freezing  injury,  which  sometimes  produces 
very  similar  symptoms,  but  usually  is  otherwise  distin- 
guishable. 

These  internal  discolorations  are  not  decay  and  do  not 
impair  the  food  value  of  the  tuber,  but  affected  portions 
usually  are  rejected  in  the  preparation  of  potatoes  for  the 
table. 

Ref.  (49);  (50). 

POTATO:     FREEZING    INJURY. 

Cause :  Exposure  to  low  temperatures  in  the  soil  or  dur- 
ing harvest,  transit,  or  storage. 

The  symptoms  of  freezing  injury  are  varied  and  complex 
and  may  be  general,  appearing  in  all  the  tissues  of  a  tuber, 
or  local  and  restricted  to  sharply  limited  regions  of  the 
tuber.  They  depend  upon  the  variety,  maturity,  and  indi- 
viduality of  the  potato  affected,  upon  the  varying  predispo- 
sition of  the  several  tissues  of  the  tuber  to  freezing  injury, 
upon  the  temperature  to  which  the  tuber  was  exposed,  and 
upon  the  rate  of  fall  of  the  temperature  as  well  as  the  dura- 
tion of  the  exposure.  The  symptoms  also  depend  upon  the 
interval  between  the  time  of  injury  and  examination  of  the 
affected  tuber,  and  may  or  may  not  depend  upon  the  rate  of 
thawing  and  the  conditions  under  which  this  takes  place. 

Thoroughly  frozen  potato  tissue  no  longer  possesses  the 
natural  crispness  or  brittleness  of  the  sound  potato.  Frozen 
tissue  looks  dull  and  does  not  cut  readily  nor  with  snap. 
This  is  due  to  the  formation  of  ice  in  the  tissues.  In  the 
freezing  process,  the  cell  water  passes  out  of  the  cells  into 
the  intercellular  spaces,  the  spaces  between  the  cells,  where 
it  forms  ice  crystals.  The  extent  to  which  the  cell  water 
leaves  the  cells  depends  upon  the  point  to  which  the  tem- 
perature is  lowered,  upon  the  rate  at  which  this  takes  place, 
upon  the  duration  of  the  exposure,  and  upon  the  nature  of 
the  potato. 

The  symptoms  presented  by  thawed  potato  tissues  are 
very  perplexing.  Sometimes  in  case  of  severe  freezing,  the 
tissues  become  turgid,  blister-like,  and  swollen,  and  the  skin 
may  be  discolored.  At  other  times  they  are  quite  firm  and 
remain  intact  and,  contrasted  with  healthy  tissue,  merely 
appear  dull  and  colorless.  If  only  a  portion  of  a  tuber  was 
severely  frozen,  usually  a  purplish  band  marks  the  border 
of  the  uninjured  tissue.  When  such  a  tuber  is  cut,  the 
border  between  healthy  and  injured  tissue  generally  is 
marked  by  a  sharp  purplish  to  dark  brown  line.  However, 
this  line  is  not  always  present. 

If  no  infection  sets  in,  the  more  or  less  watery  thawed 
tissue  dries  down  to  the  consistency  of  a  rather  moist  mealy 
mass  or  a  shrunken,  dull,  grayish,  very  tough  and  leathery 
granular  mass  which  is  composed  of  shrunken  cells  and 
starch.  Very  frequently  bluish  to  black  colors  develop.  In 


56  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

this  stage  the  dried-out  starchy  remnants  of  the  tissue  are 
separated  from  the  uninjured  tissue  by  a  dark  brown  corky 
layer. 

Very  frequently  the  starchy  or  corky  layer  is  not  formed 
before  infection  with  Fusarium  takes  place,  or  it  is  subse- 
quently broken  and  admits  the  fungus.  Severe  freezing 
injury  generally  affects  all  tissues  straight  across  the  tuber, 
while  Fusarium  rot  develops  most  rapidly  in  the  pith  of  the 
tuber,  leaving  a  shell  of  cortical  tissue.  This  characteristic 
sometimes  is  of  service  in  differentiating  freezing  injury  and 
Fusarium  tuber  rot. 

Thawed  tissue,  especially  when  in  a  warm  damp  atmos- 
phere, is  predisposed  to  slimy  soft  rot.  In  fact,  most  se- 
verely frozen  potato  tissue  is  dead  and  sooner  or  later 
becomes  infected  with  the  bacteria  which  cause  this  rot. 
The  bacteria  get  into  the  watery  tissue,  which  is  an  excellent 
growing  medium  for  them,  through  breaks  in  the  skin,  and 
cause  a  slimy,  mushy,  or  soupy  rot  which  has  a  very  offen- 
sive odor.  Frequently  the  much  wrinkled  skin  of  such  tubers 
bursts,  and  the  neighboring  potatoes  are  smeared  with  the 
slimy  disintegrated  tissue  which  dries  out  grayish  and 
chalky  when  exposed  to  the  air. 

It  is  very  difficult  at  times  to  differentiate  freezing  injury 
from  injury  due  to  scalding.  This  is  especially  true  when 
the  first  or  last  freezes  of  the  season  occur. 

The  severe  general  type  of  freezing  injury  is  marked  by 
a  killing  of  all  the  cells  of  the  potato.  The  less  severe  type, 
popularly  known  as  chilling,  is  definitely  localized  and 
restricted  to  the  most  susceptible  tissues.  It  is  known  as 
freezing  necrosis.  It  appears  first  in  the  stem  end,  and  at 
times  only  the  conducting  tissues  are  killed  and  appear  yel- 
lowish-brown to  black.  Very  often  the  conducting  tissues 
in  the  pith  also  are  killed  and  appear  as  a  net  resembling 
net  necrosis.  The  storage  tissues  also  may  be  affected,  either 
in  extensive  regions,  or  in  small  pockets.  Starchy  tissues  so 
affected  are  grayish  to  steel  blue,  even  black  in  color,  gran- 
ular, and  very  tough  and  leathery. 

Sometimes  the  thawing  tissues  are  pinkish  to  red  in  color 
when  freshly  cut.  These  colors  change  quite  rapidly  in  the 
air,  becoming  gray,  brown,  or  dirty  red.  These  colors  should 
not  be  confused  with  the  pinkish  color  of  the  vascular  ring 
or  pith  tissue  of  some  of  the  red  varieties  of  potatoes.  At 
times  white  potatoes  which  have  not  been  exposed  to  low 
temperatures  also  have  a  pink  color.  Potato  tissues  when 
freshly  bruised  and  exposed  to  the  air  often  are  reddish  in 
color. 

Potatoes  subjected  to  freezing  temperatures  may  show4 
none  of  the  symptoms  enumerated  above  but  only  a  tend- 
ency to  excessive  wilting  and  flabbiness.  The  cut  tissue  may 
appear  glassy  and  abnormally  moist.  When  cooked  they 
may  turn  black  in  spots  or  may  have  a  sweet  taste.  This 


MARKET  DISEASES  OF  VEGETABLES.  57 

condition  also  is  frequently  referred  to  as  chilling  injury. 
When  potatoes  that  have  become  sweet  following  exposure 
to  low  temperatures  are  kept  at  normal  temperatures  the 
sweet  taste  disappears.  This,  is  due  to  the  fact  that  the 
increased  respiration  due  to  rise  in  temperature  oxidizes  the 
excess  of  sugars  which  accumulated  at  temperatures  of  29° 
to  34°  F.  At  these  tempertures  the  rate  of  respiration  is  cut 
down  more  than  the  rate  of  digestion  of  starch  into  sugar 
and  consequently  the  sugars  accumulate. 

It  is  very  difficult  at  times  to  differentiate  immature 
tubers  from  those  showing  the  less  severe  types  of  freezing 
injury.  In  both  cases  the  tissues  may  have  a  greenish  yellow 
color,  and  may  be  flabby  and  bitter  in  taste.  Immature 
tubers  are  also  bruised  easily  by  impact  or  pressure,  which 
causes  regions  in  the  tuber  to  resemble  chilled  tissue  so 
closely  that  a  diagnosis  is  excedingly  difficult.  It  also  is 
exceedingly  difficult  to  differentiate  between  thawed,  dried- 
out  tissues  and  bruised  tissues. 

It  seems  in  fact  that  the  presence  of  ice  in  the  tissues  is 
the  only  positive  proof  of  freezing  injury.  All  other  char- 
acteristics enumerated  as  symptoms  of  freezing  and  chilling 
injury  can  also  be  brought  about  by  other  causes. 

Slightly  affected  stock  without  extensive,  discolored, 
killed  regions  is  suitable  for  food  even  though  it  is  not  as 
palatable  as  the  uninjured.  It  shrinks  excessively  in  transit 
and  storage. 

Guarding  against  the  exposure  of  potatoes  to  tempera- 
tures under  32°  F.  will  prevent  this  type  of  injury.  Losses 
during  transit  may  be  avoided  by  careful  sorting  to  elimi- 
nate field  frozen  tubers  previous  to  shipment,  and  the  use 
of  all  proper  precautions  to  prevent  freezing  injury  during 
hauling,  loading,  and  rail  shipment.  This  involves  proper 
lining  and  preheating  of  the  car,  installation  of  false  floor- 
ing and  ends,  and  an  adequate  heating  apparatus  regulated 
during  transit  so  as  to  avoid  both  freezing  and  black  heart 
injury. 

Ref.  (33a). 

POTATO:     BLACK    HEART. 

Cause :    High  temperature  or  insuffcient  aeration. 

The  symptoms  of  black  heart  vary,  depending  upon 
whether  the  potatoes  are  exposed  to  high  temperatures  with 
an  adequate  air  supply,  or  to  high  or  normal  temperatures 
with  an  insufficient  air  supply.  In  the  former  case,  no  ex- 
ternal symptoms  develop ;  in  the  latter,  both  external  and 
internal  symptoms  appear. 

The  external  symptoms  of  black  heart  are  moist  areas  on 
the  surface  which  may  be  purplish  at  first  but  turn  brown 
and  black  in  a  short  time.  The  internal  symptoms  are  a 
dark  gray  to  purplish  discoloration  which  later  becomes 
jet-black.  The  discolored  areas  are  usually  sharply  set  off 
from  the  healthy  tissue. 


58  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

Generally  the  discoloration  is  restricted  to  the  heart  of 
the  tuber,  but  frequently  it  radiates  to  the  exterior  as  well. 
It  may  also  appear  on  one  side  of  a  potato  if  this  was  ex- 
posed to  a  stove  in  a  railroad  car  or  in  the  storage  house. 
The  discolored  regions  may  appear  in  zones  in  the  periph- 
eral parts  and  may  be  absent  or  less  evident  in  the  center. 
In  advanced  stages,  the  affected  tissue  dries  out  and  forms 
cavities.  In  case  cavities  develop,  these  may  be  differenti- 
ated from  true  hollow  heart  by  their  black  lining  of  killed 
tissue. 

Exposure  of  potatoes  in  the  field  or  in  storage  or  transit 
for  a  day  to  temperatures  of  90°  to  104°  F.  causes  this 
injury.  Potatoes  lying  in  a  very  hot  soil  or  lying  on  the  soil 
after  digging  may  show  it.  More  generally  the  injury  is 
caused  in  stove-heated  cars  or  by  storing  potatoes  at  45°  to 
50°  F.  in  piles  deeper  than  6  feet.  In  stove-heated  cars,  the 
injury  usually  is  most  severe  near  the  stove  and  at  the  top 
of  the  load. 

Black  heart  injury  predisposes  affected  tissues  to  slimy 
soft  rot.  The  heated,  killed  and  watery  tissues  offer  excel- 
lent growing  conditions  for  bacteria. 

Black  heart  does  not  impair  the  food  value  of  non-affected 
tissues. 

Prevention  of  this  injury  in  cars  involves  proper  ventila- 
tion, protection  of  the  load  near  the  stove  with  tin  sheeting, 
and  careful  attention  to  the  fire.  The  temperature  should 
never  go  over  60°  or  70°  F. 

The  injury  can  be  prevented  in  storage  places  by  provid- 
ing proper  ventilation  and  by  storing  tubers  in  piles  not 
deeper  than  6  feet. 

Ref.  (1);  (68). 

POTATO:     SCALD. 

Cause :    Exposure  to  the  hot  sun. 

Scald  on  potatoes  may  appear  first  as  large  blisters  which 
soon  become  sharply  depressed  or  as  slightly  bleached  areas 
with  a  very  irregular  and  lobed  margin  of  a  darker  metallic 
color.  Upon  cutting  such  a  tuber,  it  is  found  that  a  shallow 
surface  layer  of  tissue  has  been  killed.  This  killed  tissue  is 
dull  gray  in  color,  and  is  separated  from  the  uninjured  tissue 
by  a  brown  and  very  irregular  line.  The  killed  tissue,  if  not 
infected,  dries  out  and  becomes  tough  and  leathery. 

In  many  cases,  more  of  the  tuber  is  involved,  both  in  sur- 
face area  and  depth  of  the  killed  tissue.  This  type  has  been 
tentatively  named  "deep  scald,"  and  shows  much  more  dis- 
coloration than  the  ordinary  scald.  Bluish  black  patches 
often  surround  the  lenticels,  and  the  killed  tissue  darkens 
very  rapidly  when  cut  surfaces  are  exposed  to  the  air. 

Scald  differs  from  late  blight  tuber  rot  in  that  the  affected 
tissue  is  not  brown  in  color,  and  in  the  sharp  line  of  demarca- 
tion between  the  dead  and  the  living  tissue.  Scald  differs 
from  freezing  injury  in  its  much  more  irregular  surface  out- 


MARKET  DISEASES  OF  VEGETABLES.  59 

line  and  in  the  more  irregular  plane  of  separation  between 
killed  and  sound  tissue.  At  certain  seasons,  it  may  be  very 
difficult  to  make  this  differentiation  positive  without  rather 
careful  inspection  of  car  lots.  Freezing  injury,  however, 
should  be  accompanied  by  other  unmistakable  symptoms. 

Scald  of  potato  is  probably  caused  by  exposure  of  newly 
dug  tubers  to  the  hot  sun  in  the  field. 

Scald  is  of  the  highest  importance  from  the  market  point 
of  view.  The  killed  tissue  is  very  subject  to  the  attacks  of 
rot-producing  organisms  such  as  Fusarium  and  especially 
the  bacteria  of  slimy  soft  rot.  In  the  Chicago  market  in  the 
summer  of  1918,  there  were  enormous  losses  due  to  slimy 
soft  rot  following  scald  in  shipments  of  potatoes  from  the 
South  and  the  entire  Mississippi  Valley. 

It  is  not  advisable  to  ship  potatoes  showing  scald  because 
of  their  extreme  predisposition  to  slimy  soft  rot  during 
transit. 

POTATO:     SALT    INJURY. 

Cause :  Contact  of  potatoes  with  the  floor  or  walls  of  a 
car  in  which  fertilizers,  salt,  or  salted  hides  have  been 
shipped. 

Usually  the  side  of  the  potato  in  contact  with  the  floor  or 
wall  is  flattened,  and  the  injured  tissue  is  soft  and  flabby 
and  at  times  semi-watery.  At  times  the  injured  tissue  is  firm 
and  leathery.  Before  the  air  has  free  access  to  the  tissue  it 
usually  is  colorless.  After  a  short  exposure  to  the  air  if  not 
infected  the  injured  tissues  become  brown  to  black,  and 
begin  to  dry  out.  The  exterior  of  the  injured  region  gener- 
ally is  black.  Frequently  the  injured  tissue  has  a  distinct 
salty  taste,  and  salt  injury  may  be  thus  diagnosed. 

Tubers  affected  with  salt  injury  are  predisposed  to  slimy 
soft  rot,  and  generally  become  infected  and  soupy  if  not 
removed  promptly  from  the  car. 

POTATO:     SUNBURN. 

Cause :  Exposure  of  tubers  to  light,  either  in  the  field,  or 
during  harvest,  shipment  and  storage. 

Sunburn  is  marked  by  a  green  discoloration  of  the  surface 
layers,  and  in  severe  cases,  of  the  interior  portions  of  the 
tuber. 

Sunburn  occurs  in  potatoes  of  all  varieties  upon  prolonged 
exposure  to  the  light.  It  is  common  in  eastern  stock  shipped 
in  midsummer. 

Affected  stock  is  bitter  and  unfit  for  food. 

POTATO:     BRUISES,    CUTS,    AND    SPLITS. 

Cause:     Mechanical  injury. 

Bruises  may  be  superficial  or  internal.  The  most  common 
type  of  bruise  occurs  in  immature  potatoes  whose  tissues 
are  very  tender  and  crisp,  and  consequently  are  easily 
broken  either  by  pressure  or  by  friction.  Often  an  immature 


60  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

tuber  is  gouged  by  rubbing  against  the  container  or  by  being 
walked  upon.  In  either  case,  the  result  is  a  loss  of  water 
by  the  injured  cells,  leaving  a  solid,  grayish,  starchy  deposit. 
At  times  this  deposit  is  black,  and  externally  the  bruised 
areas  often  appear  black.  These  types  of  bruising  are  very 
common  in  potatoes  grown  under  irrigation.  The  injury 
due  to  gouging  is  more  severe  than  peeling  or  feathering 
though  it  usually  is  due  to  the  same  causes. 

Often  potatoes  are  bruised  or  crushed  by  impact  or  by 
the  weight  of  the  load.  In  addition  to  the  injuries  above 
described,  impact  or  pressure  may  cause  symptoms  which 
may  be  wholly  internal  or  may  be  indicated  externally  only 
by  small,  slightly  sunken  spots.  At  times  these  internal  in- 
juries resemble  those  due  to  freezing  and  consist  of  small 
pockets  of  grayish,  starchy  masses,  the  remnants  of  rup- 
tured, dried-out  cells. 

Most  of  the  cuts  in  potatoes  are  caused  by  digging  imple- 
ments, and  by  the  pernicious  custom  of  handling  potatoes 
with  steel  shovels  or  forks.  Cuts  may  be  broad  and  shallow 
or  very  deep. 

If  the  cut  or  bruised  tissue  has  an  opportunity  to  dry  out 
rapidly  the  injury  may  be  sealed  by  a  grayish  granular 
deposit  of  starch,  and  later  by  a  brown  layer  of  cork.  Very 
often,  however,  especially  under  moist  conditions,  Fusarium 
gets  a  foothold  before  the  bruised  or  cut  tissue  is  healed.  It 
may  also  enter  through  subsequent  breaks  in  the  dry  starch 
layer.  In  very  hot  weather,  especially  in  southern  potatoes, 
slimy  soft  rot  gets  a  start  in  bruises  and  cuts.  Shallow, 
broad,  or  smooth  cuts  are  less  subject  to  infection  than  those 
which  are  deep  and  ragged. 

Potatoes  often  are  fractured  by  pressure  or  by  impact. 
Careless  throwing  about  of  potatoes,  heavy  loading,  walking 
upon  potatoes,  and  similar  rough  treatment,  are  responsible 
for  these  fractures  or  so-called  splits.  These  may  be  visible 
externally  or  they  may  be  wholly  internal.  In  either  case 
the  surfaces  of  the  fracture  are  lined  with  a  deposit  of  starch 
or  a  brown  layer  of  corky  tissue.  At  times  freshly  dug 
potatoes  develop  splits  if  they  dry  out  too  rapidly. 

Bruised,  cut,  or  split  potatoes  are  suitable  for  food,  though 
the  injuries  necessitate  very  appreciable  losses  in  paring. 
Their  presence,  however,  lowers  the  market  value  of  a 
shipment. 

These  mechanical  injuries  generally  are  ports  of  entry  for 
fungi  and  bacteria  which  cause  tuber  rots.  In  most  cases  of 
Fusarium  tuber  rot,  the  infection  starts  in  such  injuries.  In 
the  early  part  of  the  shipping  or  storage  period,  it  is  impos- 
sible without  a  cultural  test  to  determine  whether  a  me- 
chanical injury  will  remain  merely  an  injury  or  develop  a 
tuber  rot.  However,  as  the  season  progresses,  the  rot  symp- 
toms become  more  pronounced. 

This  type  of  injury  with  its  frequently  disastrous  conse- 
quences could  be  prevented  if  it  were  constantly  borne  in 


MARKET  DISEASES  OF  VEGETABLES.  61 

mind  that  potatoes  consist  of  living  cells  and  should  not  be 
handled  like  stones. 

POTATO:    ENLARGED    LENTICELS. 

Cause :  Excessive  water  supply  during  the  growing  season. 

This  is  marked  by  flat,  pimple-like  swellings,  which  occur 
at  the  lenticels  of  tubers.  These  swellings  are  formed  by 
proliferation  of  cells  lining  the  cavity  of  lenticels.  Normally 
these  cells  remain  dormant  but  they  may  enlarge  and  divide 
if  potatoes  are  grown  in  very  wet  soil  or  if  the  soil  becomes 
waterlogged  after  the  tubers  are  formed.  If  this  process 
continues  long  enough  a  mass  of  cells  protruding  above  the 
tuber  surface  is  formed. 

At  first  these  cells  are  quite  soft,  whitish  in  color,  and 
quite  easily  rubbed  off.  Later  they  harden  and  become 
brown  and  corky. 

Potatoes  showing  enlarged  lenticels  are  objectionable 
because  of  bad  appearance  of  the  stock.  Their  food  value 
is  not  impaired,  since  the  swellings  are  superficial. 

POTATO:    FLEA-BEETLE    DISEASE. 

Cause:  The  larva  of  the  flea  beetle  (Epitrix  cucumeris 
Harr.). 

In  the  simplest  cases  flea-beetle  injury  is  marked  by  corky 
pimples  or  raised  places  on  the  tuber.  At  times  the  surface 
of  such  pimples  is  slightly  broken.  In  the  more  Complex 
and  advanced  stages  the  surface  of  the  tuber  is  a  mass  of 
pimples  and  of  channels  or  furrows  formed  by  breaking  of 
the  skin.  The  margins  of  such  furrows  and  channels  fre- 
quently are  elevated  and  swollen  so  that  the  whole  furrow 
stands  above  the  surface  of  the  tuber.  This  type  of  injury 
frequently  is  known  as  worm  tracks. 

By  cutting  into  the  pimples  or  furrows  brown,  tough 
splinters  of  corky  tissue  are  found  extending  perpendicu- 
larly into  the  tuber  tissue.  Sometimes  these  splinters  are  a 
fourth  of  an  inch  in  length.  Their  presence  serves  to  differ- 
entiate the  simple,  pimple  stage  of  flea-beetle  injury  from 
slight  nematode  injury,  and  the  furrowed  type  from  other 
tuber  diseases  such  as  scab,  grub  injury,  or  wire-worm 
injury. 

Flea-beetle  injury  is  most  frequent  in  Colorado  potatoes. 
It  injures  the  appearance  of  potatoes  and  generally -necessi- 
tates very  deep  paring. 

POTATO:    NEMATODE    DISEASE. 

(See  Nematode  Disease). 

RADISH:     BLACK    ROOT. 

Cause:     A  fungus   (Rheosporangium  aphanidermatum). 

This  disease  of  radish  roots  is  characterized  by  blackened 
regions  of  varying  size  which  may  be  rather  superficial,  or 
may  extend  deeply  into  the  root.  The  darkened  tissue  is 


62  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

firm  and  not  disintegrated.  The  lesions  are  often  cracked 
or  fissured  on  the  surface  as  a  result  of  root  growth,  and 
may  be  accompanied  by  some  disfiguration  of  the  root  due 
to  checked  growth. 

This  disease  is  of  widespread  occurrence.  Both  red  and 
white  varieties  are  susceptible.  The  fungus  persists  in  the 
soil  and  often  causes  damping-off  of  seedlings. 

Badly  affected  roots  often  are  found  in  the  market,  but 
are  not  considered  edible,  and  their  presence  lowers  the 
value  of  the  bunch. 

Control  involves  crop  rotation  or  soil  sterilization.  Badly 
affected  roots  should  not  be  sent  to  market. 

Ref.  (16). 

RADISH:     MISCELLANEOUS    DISEASES. 

DOWNY    MILDEW. 

Cause:    A  fungus  (Peronospora  parasitica). 

Downy  mildew  causes  angular  spots  on  the  leaves, 
bounded  by  the  larger  veins.  These  spots  are  yellow  in  color 
when  viewed  from  above,  and  the  under  surface  is  covered 
with  a  white  felt-like  outgrowth  of  mold. 

This  disease  often  is  found  in  the  market  but  is  of  no 
importance  since  the  root  is  not  attacked. 

WHITE    RUST. 

Cause:    A  fungus  (Cystopus  candidus). 

The  symptoms  of  this  disease  on  the  leaves  are  small, 
irregular  lesions  bearing  on  the  under  surface  smooth,  pure 
white,  porcelain-like  cushions  or  blisters.  These  rupture, 
allowing  the  spores  to  escape,  and  the  lesions  are  then 
recognizable  by  the  torn  edge  of  the  empty  pustule.  Often 
these  lesions  cause  marked  distortion  in  the  leaves  and  other 
affected  parts. 

Since  this  disease  does  not  occur  on  the  roots,  it  is  of  no 
importance  in  the  market. 

ROOT    ROT. 

Cause:    A  fungus  (Rhizoctonia). 

This  disease  is  marked  by  a  rather  large  brown  circular 
lesion  on  the  side  of  the  root  in  which  the  tissue  is  rotted 
as  in  watery  soft  rot. 

This  has  been  found  occasionally  in  the  market. 

NEMATODE  DISEASE. 

(See  Nematode  Disease). 

RADISH;  SLIMY  SOFT  ROT;  BACTERIAL  ROT. 

(See  Slimy  Soft  Rot). 

RUTABAGA:    DRY    ROT. 

(See  Radish  Root  Rot). 


MARKET  DISEASES  OF  VEGETABLES.  63 

RUTABAGA:    GRAY    MOLD    ROT;    BOTRYTIS    ROT. 

(See  Gray  Mold  Rot) . 

RUTABAGA:    SLIMY    SOFT    ROT;    BACTERIAL    ROT. 

(See  Slimy  Soft  Rot). 

RUTABAGA:  WATERY  SOFT  ROT;  SCLEROTINIA  ROT. 

(See  Watery  Soft  Rot). 

RUTABAGA:    NEMATODE    DISEASE. 

(See  Nematode  Disease). 

SALSIFY:    WATERY    SOFT    ROT;    SCLEROTINIA    ROT. 

(See  Watery  Soft  Rot  and  Beet  Watery  Soft  Rot). 

SPINACH:    SLIMY    SOFT    ROT;    BACTERIAL    ROT. 

(See  Slimy  Soft  Rot). 

SQUASH:    RHIZOPUS    ROT. 

(See  Rhizopus  Rot). 

SWEET    POTATO:     BLACK    ROT. 

Cause:    A  fungus  (Sphaeronema  fimbriatum). 

Black  rot  is  characterized  by  greenish  to  nearly  black, 
circular,  depressed  spots,  varying  in  size  from  y%  to  2  inches 
in  diameter.  At  times  the  spots  are  very  irregular,  occur- 
ing  in  bruises  and  injured  places.  The  lesions  are  shallow, 
rarely  penetrating  to  the  heart  of  the  root,  and  the  affected 
tissue  is  quite  firm  and  tough.  Often  at  the  center  of  the 
spots  small,  black  bodies  are  developed,  which  appear  at 
times  as  dense  masses  of  small,  black  bristles.  These  are  the 
fruiting  bodies  or  pycnidia  of  the  fungus.  Wetting  the  sur- 
face of  the  lesion  will  bring  out  better  these  distinguishing 
characteristics. 

Black  rot  is  of  common  occurrence  in  all  sweet  potato 
regions.  The  roots  become  infected  in  the  field,  often 
through  wounds.  The  diseased  areas  may  enlarge  in  stor- 
age or  transit,  where  overheating  and  lack  of  ventilation 
favor  the  progress  of  the  disease.  "Generally,  affected  stock 
is  culled  out  and  is  not  sent  to  the  markets. 

Affected  stock  is  unfit  for  table  use  since  the  diseased 
tissue  is  very  bitter.  When  cooked,  the  entire  root  has  a 
bitter  flavor.  Diseased  sweet  potatoes  also  are  unsuitable 
for  seed  purposes,  since  black  rot  is  spread  by  planting  in- 
fected seed  roots. 

Ref.  (24);  (27);  (70). 

SWEET    POTATO:    SOIL    ROT. 

Cause:    A  slime  mold  (Cystospora  batata). 
The  symptoms  of  this  disease  are  small,  circular,  sunken 
spots  about  one-half  inch  in  diameter  in  which  the  tissue 


64  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

has  dried  out  and  cracked.  The  lesions  may  appear  as  cir- 
cular pits  or  depressions  from  which  the  diseased  tissue  has 
fallen  out.  There  may  be  some  constriction  of  the  root 
where  such  lesions  are  located. 

Infection  occurs  in  the  field  and  the  disease  does  not  pro- 
gress in  storage. 

The  economic  importance  of  soil  rot  is  due  to  the  fact  that 
it  reduces  the  yield  and  disfigures  the  roots. 

Ref.  (69). 

SWEET   POTATO:     SCURF. 

Cause:    A  fungus  (Monilochaetes  infuscans). 

Scurf  is  marked  by  small,  circular,  dark  clay-colored  spots 
on  the  skin  of  the  root,  which  may  unite  to  form  large 
blotches.  The  spots  are  only  skin-deep.  In  advanced 
stages,  the  skin  turns  to  a  deep  brown  color  and  becomes 
wrinkled  and  rough. 

Scurf  occurs  in  practically  all  sweet  potato  growing 
regions. 

Infection  takes  place  in  the  field,  but  the  spots  may  de- 
velop in  storage.  The  disease  does  not  spread  from  one  root 
to  another.  The  market  value  of  diseased  stock  is  slightly 
reduced  because  of  its  unsightliness. 

Ref.  (24);  (27). 

SWEET    POTATO:     SOFT    ROT. 

Cause:    A  fungus  (Rhizopus  nigricans) . 

This  rot  is  one  of  those  elsewhere  described  as  Rhizopus 
rot.  Soft  rot  develops  very  rapidly,  and  unless  checked, 
soon  involves  the  whole  root.  In  the  early  stages,  the 
affected  tissue  is  soft,  watery,  and  stringy,  and  yields  a 
brownish-yellow  liquid  when  compressed.  The  early  stage 
is  also  attended  by  an  odor  of  vinegar  or  acetic  acid.  Under 
warm,  moist  conditions,  the  characteristic  mycelium  and 
sporangia  may  appear  on  the  outside  of  the  root.  The 
affected  tissue  eventually  becomes  dry,  shrunken,  and  yel- 
lowish brown.  At  this  stage  an  aromatic  odor  may  be 
detected. 

Infection,  which  takes  place  through  wounds,  occurs 
either  in  the  field,  in  transit,  or  in  storage  and  is  favored  by 
high  temperature  and  humidity.  The  rot  progresses  and 
spreads  very  rapidly  in  transit  and  storage.  Infection  may 
set  in  at  the  end  or  the  middle  of  the  root.  In  the  former 
case,  it  is  called  soft  rot ;  in  the  latter,  if  encircling  the  root, 
ring  rot. 

Control  consists  of  careful  handling  of  the  roots  to  avoid 
wounds,  careful  sorting,  proper  curing,  and  storage  in  a  dry 
atmosphere  at  a  temperature  of  50°  F.  When  wet  weather 
prevails  during  harvest,  the  shipment  of  roots  not  properly 
dried  often  results  in  severe  losses.  An  additional  control 
measure  is  the  disinfection  of  storage  houses  and  cars  with 
copper  sulphate  or  formaldehyde. 

Ref.  (24);  (27). 


MARKET  DISEASES  OF  VEGETABLES.  65 

SWEET  POTATO:     STEM   ROT. 

Cause :  Fungi  (Fusarium  batatatis  and  F.  hyperoxy- 
sporum). 

In  stem  rot  the  end  of  the  root  is  light  and  shriveled,  and 
the  interior  has  a  deep  brown  color  and  a  peculiar  cinna- 
mon odor.  Usually,  however,  stem  rot  is  not  plainly  visible 
externally,  and  the  disease  manifests  itself  merely  by  a  dis- 
colored ring,  and  at  times  by  a  secondary  ring,  visible  in 
transverse  sections  of  the  root.  If  the  outer  part  of  the  root 
is  carefully  removed,  the  discolored  parts  appear  as  a  net- 
work of  brown  fibers  surrounding  the  heart. 

Stem  rot  is  of  widespread  occurrence  in  all  sweet  potato 
districts. 

This  disease  causes  a  wilt  of  vines  in  the  field,  and  re- 
duces the  yield.  Infection  of  the  roots  takes  place  in  the 
field,  and  the  disease  progresses  only  slightly  in  storage. 
Stem  rot  is  found  infrequently  in  the  market,  and  is  de- 
scribed here  principally  to  avoid  confusion  with  freezing 
injury,  which  it  somewhat  resembles. 

Ref.  (24). 

SWEET   POTATO:     MISCELLANEOUS    DISEASES. 

DRY    ROT. 

Cause:    Fungi  (Fusarium  species). 

This  disease  is  comparable  to  the  Fusarium  tuber  rot  of 
the  Irish  potato.  It  is  marked  by  shrunken  areas  showing 
discolored  flesh,  and  usually  starts  at  one  end  of  the  root. 
Dry  rot  is  not  common  or  of  much  importance. 

FOOT  ROT. 

Cause :    A  fungus  (Plenodomus  destruens) . 

This  is  a  storage  rot  of  some  importance.  It  follows  a 
blighting  of  plants  in  the  field.  It  is  a  firm  brown  rot  with 
pimple-like  protuberances  on  the  surface.  Foot  rot  may 
enter  roots  through  wounds  and  bruises  and  thus  cause  some 
loss  in  storage. 

Ref.  (27). 

NEMATODE  DISEASE. 

(See  Nematode  Disease). 

TOMATO:     ANTHRACNOSE. 

Cause:     A  fungus  (Colletotrichum  phomoides). 

In  its  early  stages,  anthracnose  is  characterized  by  small, 
circular,  sunken  spots  of  the  same  color  as  the  sound  tissue. 
These  lesions  enlarge  rapidly,  become  watersoaked  and 
more  sunken,  and  bear  pinkish  spore  heaps  which  often 
coalesce  to  form  a  slimy  layer.  These  spore  heaps  or  acer- 
vuli  turn  black  at  times  and  resemble  the  pycnidia  of  Phoma, 
so  that  anthracnose  may  be  mistaken  for  Phoma  lesions. 
However,  the  spore  heaps  never  are  as  definitely  rounded  as 


66  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

the  pycnidia,  and  the  pycnidia  never  are  pink.  The  centers 
of  anthracnose  lesions  are  at  first  light  brown,  and  do  not 
become  as  black  and  charry  as  those  of  Phoma  rot. 

Anthracnose  is  common  on  northern-grown  tomatoes, 
especially  New  Jersey  stock.  Green  fruit  is  rarely  affected. 

The  original  infection  takes  place  in  the  field.  The  dis- 
ease develops  in  the  field,  and  may  also  spread  and  develop 
in  transit  and  storage.  Often  this  fungus  destroys  the  entire 
fruit. 

It  is  advisable  not  to  pack  or  ship  infected  fruit  because 
it  rots  rapidly  and  is  a  menace  to  healthy  fruit. 

Ref.  (30). 

TOMATO:     BUCKEYE    ROT. 

Cause :    A  fungus  (Phytophthora  terrestria) . 

No  better  description  of  this  disease  can  be  given,  so  far 
as  the  appearance  of  the  fruit  on  the  vine  or  in  transit  is 
concerned,  than  is  implied  by  the  name  "buckeye."  In  color 
and  in  its  surface  appearance,  the  diseased  tissue  resembles 
a  horse  chestnut  very  closely.  The  color  is  grayish  to  brown, 
and  the  surface  is  uneven,  being  sunken  in  places.  The  rot 
at  first  is  firm  and  even  hard.  The  border  is  irregular  and 
not  sharply  defined,  and  often  merges  into  water-soaked, 
slightly  bleached,  green  tissue.  At  times  there  appear 
widely  separated  concentric  rings  of  more  or  less  irregular 
wavy  outline.  These  rings,  however,  are  by  no  means  a  con- 
stant accompaniment  of  the  disease.  Under  moist  condi- 
tions the  lesions  generally  are  covered  by  a  white,  fluffy 
growth  of  mold. 

In  case  concentric  rings  are  found  in  buckeye  rot,  they  are 
farther  apart  and  less  regular  in  outline  than  in  soil  rot.  In 
soil  rot,  the  mycelium  is  brown  and  may  produce  sclerotia, 
while  the  mycelium  of  buckeye  rot  is  white  and  produces  no 
sclerotia.  The  absence  of  white,  glistening  or  black  spo- 
rangia differentiates  buckeye  rot  from  Rhizopus  rot. 

This  disease  occurs  most  commonly  in  southern  tomatoes 
during  rainy  weather.  The  original  infection  takes  place  in 
the  field,  and  occurs  only  on  fruit  which  has  been  in  contact 
with  the  soil  or  close  enough  to  it  to  be  spattered  during 
rains. 

As  in  the  case  of  soil  rot,  buckeye  rot  can  be  controlled 
in  the  field  by  staking  the  vines  to  keep  them  off  the  ground. 
At  harvest  it  is  advisable  to  sort  out  diseased  fruit  because 
it  is  unsuitable  for  food  and  is  a  menace  to  healthy  stock 
since  the  fungus  passes  through  the  wrappers  from  diseased 
to  healthy  fruit. 

Ref.  (56);  (59). 

TOMATO:     NAIL-HEAD    SPOT. 

Cause:    A  fungus  (Alternaria  solani). 


MARKET  DISEASES  OF  VEGETABLES.  67 

In  the  early  as  well  as  the  later  stages,  nail-head  spot  is 
marked  by  small,  dry,  slightly  though  abruptly  sunken  scab- 
like  spots  which  are  brown  to  black  in  color. 

These  spots  or  lesions  generally  are  mere  blemishes,  and 
cause  little  damage.  The  lesions  may  be  circular  or  ellipti- 
cal and  at  times  may  coalesce  to  form  a  large,  irregularly 
shaped  area.  At  times  the  spots  on  ripening  fruits  are  sur- 
rounded by  a  green  zone  due  to  delayed  ripening  of  the 
bordering  tissue.  The  tissue  underlying  the  spot  is  not 
affected,  and  the  diseased  tissue  can  easily  be  removed  from 
the  sound  tissue  underneath.  As  the  lesion  ages,  it  often 
cracks  and  opens  the  way  for  the  entrance  of  secondary  rots 
such  as  Phoma. 

The  small  size  and  the  slightly  sunken,  flat  and  scab-like 
nature  of  the  lesions  of  nail-head  differentiate  these  from 
the  lesions  of  other  tomato  fruit  diseases,  most  of  which,  in 
contrast,  are  large  or  water-soaked,  often  deeply  sunken 
and  involve  more  rotting  of  the  tissue. 

Nail-head  spot  is  a  warm-weather  disease,  and  is  preva- 
lent on  fruit  from  the  Gulf  States.  It  is  a  serious  field  dis- 
ease, attacking  leaves,  stems  and  fruits,  and  is  known  by  the 
growers  as  early  blight.  The  fruit  is  infected  before  it 
leaves  the  field,  and  the  spots  are  visible  when  the  fruit  is 
packed.  The  spots  may  enlarge  slowly  in  transit  and 
storage. 

Spraying  will  control  the  disease  in  the  field.  In  packing 
it  is  advisable  to  sort  out  spotted  fruit  because  its  presence 
lowers  the  market  value  of  a  shipment  and  affected  fruits 
are  predisposed  to  rots. 

Ref.  (56);  (60). 

TOMATO:     PHOMA   ROT. 

Cause:     A  fungus  (Phoma  destructiva). 

In  its  early  stages,  Phoma  rot  is  marked  on  the  green  fruit 
by  minute,  slightly  sunken  circular  spots  with  a  brown  or 
black  border  and  a  lighter  center.  Later  the  center  of  the 
spot  becomes  covered  with  black  pimple-like  bodies.  These 
are  known  as  pycnidia  (singular  pycnidum).  In  the  early 
stages,  spots  on  ripe  fruit  are  water-soaked  and  concave. 
Later,  as  they  enlarge,  the  centers  become  brown  to  charry 
black,  leathery  and  firm,  and  covered  with  pycnidia.  The 
borders  are  slightly  sunken  and  water-soaked.  The  lesions 
increase  indefinitely  and  quite  rapidly  in  size  but  remain 
more  or  less  circular  and  concave. 

The  lesions  generally  occur  at  the  stem  end  of  the  tomato, 
and  the  disease  is  often  known  as  stem-end  rot.  The  spots, 
however,  are  not  confined  to  this  part  of  the  fruit,  as  the 
fungus  may  attack  the  fruit  wherever  it  is  bruised  or  in- 
jured. The  fungus  may  also  enter  through  nailhead  spots. 
Until  the  lesion  becomes  very  large,  the  underlying  brown 
or  black  tissue  is  quite  firm. 


68  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

Without  a  microscope  it  is  quite  difficult  at  times  to  differ- 
entiate the  various  rots  of  mature  tomato  fruits  caused  by 
Phoma,  Colletotrichum,  and  other  fungi.  This  is  especially 
true  when  secondary  rots  have  set  in  and  covered  up  or  con- 
fused the  typical  clear-cut  symptoms. 

It  appears,  however,  that  anthracnose  and  other  fruit  rots 
are  more  common  on  over-ripe  fruit,  and  occur  in  southern 
stock  later  in  the  season  than  does  the  Phoma  rot.  The 
slimy,  orange-pink  spore  masses  of  anthracnose  aid  in  dif- 
ferentiating it  from  Phoma  rot.  In  Phoma  rot,  slimy  spore 
masses  appear  very  frequently  at  the  openings  of  the  pycni- 
dia,  but  these  are  whitish  rather  than  pink  in  color. 

This  disease  is  most  marked  in  southern  winter-grown 
tomatoes;  that  is,  the  Cuba,  Florida,  and  California  crops. 
It  was  exceedingly  destructive  to  Cuban  tomatoes  during 
the  winter  of  1917-18,  and  to  Florida  tomatoes  during  April 
and  May  of  the  same  season. 

The  disease  occurs  on  the  vines,  where  it  is  known  as 
Phoma  blight  or  black  spot.  It  is  not  known  definitely 
whether  the  original  infection  of  the  fruit  destroyed  in  tran- 
sit occurs  in  the  field  or  in  the  packing  house.  The  disease 
develops  in  transit  and  in  the  ripening  rooms,  and  is  favored 
by  a  warm,  moist  atmosphere. 

Affected  fruit  is  subject  to  infection  with  bacteria  and 
other  fungi. 

No  satisfactory  control  of  the  disease  in  transit  and  in  the 
ripening  rooms  has  been  worked  out. 

Ref.  (32);  (56);  (60). 

TOMATO:     SOIL   ROT. 

Cause:     A  fungus  (Rhizoctonia). 

In  its  early  stages,  soil  rot  on  green  or  ripe  fruit  is  char- 
acterized by  firm,  brown  spots  which  may  be  marked  with 
concentric  rings.  Later  they  increase  in  size  and  generally 
a  brown,  firm  mat  of  mold  covers  the  older  lesions.  On 
mature  fruit  in  the  market,  soil  rot  lesions  are  large,  brown, 
water-soaked  areas  not  sunken  and  not  concentrically 
marked. 

Soil  rot  progresses  and  spreads  very  rapidly  in  transit  and 
storage,  the  fungus  passing  from  one  fruit  to  another 
through  the  wrappers.  The  most  striking  characteristic 
under  these  circumstances  is  the  plentiful  development  of  a 
coarse,  white,  and  later,  brown  mycelium  with  small  brown 
sclerotia.  The  growth  of  the  hyphae  is  of  a  peculiar  radiat- 
ing type,  resembling  densely  crowded  spokes  of  a  wheel, 
and  is  often  further  characterized  by  concentric  zones.  Very 
often  the  mycelium,  the  sclerotia,  and  the  paper  wrapper 
form  a  thick,  dry  and  hard  mat,  or  the  hyphae  may  hold  the 
wrapper  quite  firmly  to  the  fruit  so  that  shreds  of  it  remain 
when  the  fruit  is  unwrapped.  Examination  of  decayed  fruit 
in  the  market  often  reveals  the  original  soil  rot  lesion  with 
its  firm,  brown  and  concentrically  marked  center  surrounded 


MARKET  DISEASES  OF  VEGETABLES.  69 

by  water-soaked  but  firm  tissue.  Later  there  appears  the 
coarse  white  mycelium  which  turns  brown  and  forms  scler- 
otia.  The  water-soaked  areas  are  often  referred  to  by  the 
trade  as  "water  blisters." 

The  fact  that  this  rot  is  not  limited  to  the  blossom-end  of 
the  fruit,  and  is  accompanied  by  a  mycelium,  differentiates 
it  from  blossom-end  rot.  It  may  follow  blossom-end  rot, 
however.  Its  solid  mat  of  brown  mycelium  and  its  large 
lesions  differentiate  it  from  nail-head  spot.  The  brown  mat 
of  fungus  and  the  more  regular  and  more  closely  arranged 
markings  also  differentiate  soil  rot  from  the  buckeye  rot. 
Furthermore,  in  the  field,  soil  rot  always  shows  these  con- 
centric rings  while  buckeye  rot  may  not.  Soil  rot  differs 
from  Phoma  rot  by  the  absence  of  a  black  center  with  black 
pycnidia  and  from  anthracnose  by  the  absence  of  the 
orange-pink  spore  heaps. 

Soil  rot  is  especially  severe  on  Florida  tomatoes  during 
rainy  weather.  It  also  occurs  in  early  shipments  of  Cali- 
fornia tomatoes. 

The  original  infection  takes  place  from  the  soil  in  the 
field.  Fruits  touching  the  ground  or  hanging  low  enough 
to  be  spattered  by  the  soil  during  rains  are  infected.  The 
rot  develops  and  spreads  in  the  pack. 

This  disease  can  be  controlled  in  the  field  by  staking  the 
plants.  It  is  advisable  to  sort  out  diseased  fruit  in  the  pack- 
ing house,  since  affected  fruit  is  unmarketable,  unfit  for 
food,  and  a  menace  to  sound  fruit. 

Ref.  (56). 

TOMATO:     BLOSSOM-END    ROT. 

Cause:   Non-parasitic  (probably  irregular  water  supply). 

In  the  early  stages  this  disease  appears  as  a  small  spot  at 
the  blossom-end,  or  it  may  involve  the  whole  blossom  sur- 
face of  the  fruit.  At  this  stage  the  spot  looks  like  a  bruise, 
is  dark  green  in  color  and  water-soaked.  Later  it  becomes 
darker,  and  the  affected  tissue  collapses  and  becomes  firm 
and  leathery.  Sometimes  the  collapse  is  so  sharply  marked 
that  the  lesion  appears  as  a  distinct  depression.  Generally, 
however,  it  results  only  in  a  flattening  of  the  end  of  the  fruit. 
The  lesions  are  very  shallow  and  dry ;  this,  together  with  the 
restriction  of  this  injury  to  the  blossom-end,  serves  to  differ- 
entiate blossom-end  rot  from  the  buckeye  rot  of  green  toma- 
toes and  the  soil  rot  of  both  green  and  ripe  fruits  with  which 
it  might  be  confused. 

Blossom-end  rot  is  a  field  disease,  and  occurs  in  all  tomato 
growing  districts. 

Affected  tissue  is  predisposed  to  secondary  rots,  which 
develop  in  the  field,  in  transit,  and  in  storage.  The  non- 
parasitic  injury  is,  in  fact,  commonly  followed  by  fungous 
rots. 

Blossom-end  rot  has  not  been  successfully  controlled. 
Regulation  of  the  water  supply,  and  the  use  of  varieties 


70  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

suited  to  the  soil  and  climate,  are  important  points  to  con- 
sider. 

It  is  not  advisable  to  put  badly  affected  fruit  on  the  mar- 
ket. Slightly  affected  fruit,  if  not  infected  by  fungi,  can  be 
used  for  food. 

Ref.  (3). 

TOMATO:     MOTTLING. 

Cause :    Unknown,  probably  mosaic. 

This  disease  is  characterized  by  a  more  or  less  extensive 
brown  discoloration  of  the  surface  of  the  fruit  in  which  the 
affected  areas  show  great  diversity  of  pattern,  such  as  cir- 
cular spots,  blotches,  loops,  and  streaks.  The  affected  areas 
are  somewhat  sunken  and  on  green  fruits  the  brown  color 
may  be  absent.  The  affected  tissue  is  firm  and  hard.  The 
entire  thickness  of  the  wall  and  even  portions  of  the  septa 
(partitions)  are  involved.  It  seems  that  portions  at  least 
of  the  affected  tissues  are  dead.  At  any  rate,  diseased  fruits 
will  not  ripen  properly  in  the  ripening  rooms,  and  the 
browned  or  sunken  areas  commonly  become  infected  with 
various  fungi.  *  The  disease  resembles  in  some  ways  the 
mosaic  disease  of  cucumbers. 

In  shipments  of  California  tomatoes  received  in  Chicago 
during  the  fall  of  1918,  this  disease  was  undoubtedly  the 
most  important  loss-producing  factor,  the  loss  amounting  in 
some  cases  to  50  per  cent  or  more. 

No  control  is  known.  Since  the  symptoms  are  evident  on 
the  green  fruits,  it  is  advisable  to  sort  out  affected  stock 
before  shipment,  as  it  is  a  total  loss  at  destination. 

TOMATO:    BLACK    ROT. 

Cause:    A  fungus  (Alternaria). 

The  most  striking  symptom  of  this  disease  is  the  conspicu- 
ous, black  velvety  growth  of  the  fungus  on  the  lesions.  The 
disease  generally  occurs  on  ripe  fruit,  where  it  causes  a 
slowly  progressing  rot.  The  fungus  probably  gains  entry 
through  wounds  and  growth  cracks. 

TOMATO:    CATFACE. 

Cause :    Unknown,  probably  varietal. 

In  this  disease  the  blossom  end  of  the  fruit  is  badly  mis- 
shapen or  puckered,  probably  due  to  the  imperfect  develop- 
ment of  an  area  which  at  maturity  is  represented  by  an 
irregular  leathery  scar.  Occasionally  secondary  rots  occur 
in  the  malformed  areas.  The  presence  of  catface  in  ship- 
ments lowers  their  market  value. 

TOMATO:    GROWTH   CRACKS. 

Cause :    Probably  arrested  and  resumed  growth. 
These  are  rather  deep  ruptures  or  cracks  radiating  from 
the  stem  end.     Occasionally  they  are  arranged  concentric- 


MARKET  DISEASES  OF  VEGETABLES.  71 

ally  about  the  stem  end.    They  seldom,  if  ever,  occur  in  the 
blossom  half  of  the  fruit. 

These  cracks  are  actual  wounds.  Either  before  or  after 
the  fruit  leaves  the  field,  they 'are  very  likely  to  become  in- 
fected with  rot-producing  organisms.  From  the  market 
point  of  view,  growth  cracks  assume  a  very  great  impor- 
tance because  rots  so  frequently  start  in  them. 

TOMATO:    RING    ROT. 

Cause:     A  fungus  (Melanconium). 

A  large,  circular,  flattened  lesion,  very  conspicuous  be- 
cause of  its  broad,  concentric  rings,  is  characteristic  of  this 
disease.  The  background  color  is  brown  and  the  center  and 
the  margin  may  be  slightly  elevated.  Under  moist  condi- 
tions acervuli  (singular  acervulus) ,  the  fruiting  bodies  of  the 
fungus,  appear.  The  spores  which  exude  from  them  fre- 
quently germinate  and  the  resultant  white  mycelial  growth 
covers  the  center  of  the  lesions.  The  rotted  tissue  is  firm, 
but  affected  fruits  are  worthless.  Ring  rot  has  been  found 
to  a  limited  extent  in  Cuban  tomatoes. 

Ref.  (72a). 

TOMATO:    FUSARIUM    ROT. 

Cause:     A  fungus  (Fusarium). 

The  differentiating  symptom  of  this  disease  is  a  heavy, 
compact,  pinkish-white  growth  of  the  fungus  on  the  lesions. 
The  advancing  edge  of  the  lesions  frequently  is  free  from 
visible  fungous  growth  and  is  water-soaked  and  shrunken. 
The  fungus  probably  attacks  the  fruit  through  wounds. 

TOMATO:    RHIZOPUS    ROT. 

Cause:     A  fungus  (Rhizopus  nigricans). 

The  general  features  of  this  disease  have  been  taken  up 
under  the  discussion  of  Rhizopus  rot.  It  is  a  very  soft,  leaky 
rot.  Affected  fruit  has  an  acid  odor  and  when  ripe  usually 
has  a  bleached  appearance.  This  rot  rarely  is  found  on 
green  fruit. 

The  fungus  attacks  the  fruit  through  breaks  in  the  skin. 
These  may  be  due  to  careless  handling  and  so  minute  as  to 
be  invisible  to  the  unaided  eye,  or  they  may  result  from  skin 
pricks,  nail  injury,  or  mashing  in  packing  or  transit.  The 
disease  spreads  in  transit,  the  fungus  growing  through  the 
wrapper  from  diseased  to  healthy  fruit. 

Ref.  (56). 

TOMATO:    FOUL-SMELLING    ROTS. 

Cause:    Bacteria  and  fungi. 

The  various  tomato  rots  that  are  accompanied  by  foul 
odors  have  not  been  studied  sufficiently  to  be  differentiated 
and  named. 

TOMATO:    SUN-SCALD. 

(See  Sun-scald). 


72  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

TURNIP:    GRAY    MOLD    ROT;    BOTRYTIS    ROT. 

(See  Gray  Mold  Rot). 
TURNIP:    SLIMY   SOFT   ROT;    BACTERIAL   ROT;    SOFT    ROT. 

(See  Slimy  Soft  Rot). 

WATERMELON:  ANTHRACNOSE. 

Cause:     A  fungus  (Colletotrichum  lagenarium). 

In  its  early  stages,  anthracnose  is  characterized  by  small 
circular  raised  welts  on  the  rind,  dark  green  in  color.  As 
these  increase  in  size,  the  centers  turn  brown,  become 
sunken,  and  under  moist  conditions  the  pink  acervuli  of  the 
fungus  are  formed.  As  a  lesion  enlarges,  the  center  becomes 
more  sunken,  often  turns  black,  and  eventually  the  surface 
cracks,  exposing  the  rotted  tissue  or  a  cavity  underneath. 
The  fungus  causes  a  rather  slowly  advancing  dry  rot  of  the 
rind  tissue,  and  finally  penetrates  the  edible  pulp.  Under 
extremely  dry,  hot  conditions,  such  as  occur  in  California 
during  the  melon  harvest,  the  lesions  may  remain  in  the 
blister  or  nail-head  stage. 

Anthracnose  is  a  serious  disease  of  the  vines  and  fruits  in 
the  field.  The  fungus  is  spread  with  the  seed,  overwinters 
in  the  soil,  and  spreads  in  the  field  during  rainy  weather. 
This  is  the  same  fungus  which  causes  cucumber  and  musk- 
melon  anthracnose. 

Many  fruits  are  rendered  worthless  in  the  field.  The  dis- 
ease is  also  present  in  almost  every  car  of  melons  shipped 
north  as  a  result  of  field  infection  which  may  or  may  not 
have  been  detectable  at  the  time  of  loading.  The  lesions 
enlarge  during  transit  and  not  only  seriously  impair  the 
appearance  of  the  fruit,  but  open  the  way  for  the  entrance 
of  other  rot-producing  organisms. 

Anthracnose  is  prevalent  throughout  the  southern  melon 
regions  and  the  Ohio  Valley.  It  is  the  source  of  great  losses 
in  the  field,  in  transit,  and  in  the  market. 

The  disease  can  be  controlled  in  the  field  by  crop  rotation, 
use  of  disease-free  seed,  and  spraying  with  Bordeaux  mix- 
ture. 

Ref.  (58). 

WATERMELON:     STEM-END    ROT. 

Cause:    A  fungus  (Diplodia). 

This  is  a  rapidly  progressing  soft  rot  of  the  stem  end  of 
the  melon,  marked  externally  by  a  brown  discoloration  and 
shrivelling  followed  by  the  development  of  abundant  black 
pycnidia  or  a  dark,  gray,  moldy  outgrowth  of  the  fungus. 
Whitish  spore  masses  are  often  discharged  from  the  pycni- 
dia. The  disease  usually  affects  the  stem-end  of  fruit,  but 
occurs  also  at  wounds  and,  in  the  field,  as  a  blossom-end  rot. 

While  the  rot  is  rather  common  in  the  field,  diseased 
fruits  are  not  often  shipped,,  and  it  seems  quite  likely  that 


MARKET  DISEASES  OF  VEGETABLES.  73 

infection  in  the  case  of  the  stem-end  rot  found  in  the  market 
takes  place  through  the  end  of  the  stem  after  it  is  cut.  The 
rot  then  develops  with  extreme  rapidity  during  transit. 

This  is  the  most  important  rot  of  watermelons,  and  is 
rather  general  in  southern  grown  stock,  causing  very  heavy 
losses  in  some  cars. 

Stem-end  rot  as  it  occurs  in  transit  can  be  prevented  by 
proper  treatment  of  the  melons  at  the  time  of  loading.  After 
a  tier  of  melons  is  in  place,  the  ends  of  the  stems  are  cut  off 
and  a  paste  made  of  starch  and  copper  sulphate  is  applied 
to  the  freshly  cut  surfaces.  This  prevents  infection  by  the 
fungus. 

Ref.  (42);  (51). 

WATERMELON:     MISCELLANEOUS    DISEASES. 
BLOSSOM-END  ROT. 

Cause:    Unknown  (not  parasitic). 

This  disease  appears  as  a  flattened,  dry,  leathery,  black- 
ened spot  about  as  big  as  a  silver  dollar,  at  the  blossom-end 
of  the  fruit.  The  tissues  underneath  are  sound  unless  the 
killed  area  becomes  infected  with  some  fungus  such  as  the 
Diplodia  of  stem-end  rot,  which  is  a  common  secondary 
invader. 

While  the  cause  of  this  trouble  has  not  been  demon- 
strated, it  is  quite  likely  that  it  is  due  to  an  unbalanced 
water  supply  as  in  the  similar  disease  of  tomatoes.  Although 
of  minor  importance  in  the  market,  it  may  .open  the  way  to 
rot-producing  fungi. 

Ref.  (51). 

CHEMICAL    INJURY   AND    ABRASION. 

Cause :    Contact  with  the  walls  or  floors  of  cars. 

This  injury  consists  of  large  brown  sunken  areas  or 
gouged  channels  in  the  rind.  It  is  most  common  in  cars 
previously  used  for  chemicals  such  as  fertilizers,  especially 
where  some  shifting  of  the  load  has  occurred.  Sometimes 
fungi  gain  entrance  through  these  injuries,  and  cause  decay. 

Compared  with  stem-end  rot,  this  trouble  is  not  of  com- 
mon occurrence. 

Ref.  (51). 


